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My English friend Margaret laughed at me when I asked how you are supposed to eat a custard slice without the custard coming out the sides. Nobody in Britain has ever managed it, she said. The custard slice, which plenty of people call the vanilla slice, sits in the window of nearly every bakery in England: a tall block of set vanilla custard between two layers of crisp puff pastry, with smooth white icing on top. Margaret says you can judge a bakery by it. The pastry must shatter, and the custard must be thick enough to stand up when you cut it, but still cold, soft and creamy when you bite.
It has traveled well, too. In Australia people take the vanilla slice so seriously that there is a national competition every year to find the best one in the country. The heart of it is the custard, and the question everybody asks is how thick it has to be. The answer: thick enough that when you lift the whisk out of the pan, the custard falls back in heavy ribbons that hold their shape on the surface for a few seconds, and it bubbles slowly like thick porridge. That takes a generous amount of cornstarch and a full minute of boiling once it thickens. Undercook it and it oozes flat; cook it properly and it sets firm enough to slice.
Why this custard slice works
- Pastry baked between two trays. Weighing the puff pastry down while it bakes makes it rise crisp and flaky but flat and even, so the slice stacks neatly.
- Cornstarch and egg yolks. Cornstarch gives the custard the strength to stand up; the yolks give it richness and color.
- A full minute at the boil. Cornstarch only reaches full thickening power once it boils. Stopping early leaves a custard that will not set.
- Set cold overnight. A long chill firms the custard all the way through, so it cuts clean.
Ingredients
Makes one 8 inch square pan, cut into 9 slices. The measurements are in US cups with grams in brackets.
For the pastry
- 1 package (about 17 ounces, 490g) frozen all-butter puff pastry, 2 sheets, thawed
For the custard
- 3 cups whole milk (720ml)
- 1 cup heavy cream (240ml)
- 3/4 cup granulated sugar (150g)
- 2/3 cup cornstarch (85g)
- 6 large egg yolks
- 2 tablespoons unsalted butter (28g)
- 1 tablespoon vanilla extract, or the seeds of 1 vanilla bean
- Pinch of fine salt
For the icing
- 1 1/2 cups powdered sugar (180g)
- 2 to 3 tablespoons milk
- 1/2 teaspoon vanilla extract
Choose puff pastry made with butter; it bakes crisper and tastes better. If your sheets are a different size, roll each one to a little larger than 8 inches square before baking and trim it to fit the pan afterwards.
How to make custard slice
Bake the pastry
- Heat the oven to 400 degrees (200°C). Line two baking sheets with parchment.
- Lay each pastry sheet on a lined baking sheet and prick all over with a fork. Cover with another sheet of parchment and set a second baking sheet on top to weigh it down.
- Bake for 20 minutes, then remove the top tray and parchment and bake 5 to 10 minutes more, until deep golden and crisp. Cool completely.
- Line an 8 inch square pan with plastic wrap or parchment, leaving an overhang. Trim both pastry sheets to fit the pan exactly. Lay one in the bottom, smooth side down.
Make the custard
- Heat the milk and cream in a saucepan until steaming.
- In a bowl, whisk the sugar, cornstarch, egg yolks and salt into a smooth thick paste. Slowly whisk in the hot milk.
- Pour everything back into the pan and cook over medium heat, whisking constantly and scraping the corners, until it thickens. Keep whisking until it bubbles slowly in the center, then cook a full minute more. It is thick enough when it falls from the whisk in heavy ribbons that hold their shape on the surface for a few seconds.
- Off the heat, whisk in the butter and vanilla. Pour the hot custard over the pastry in the pan and smooth it level. Lay the second pastry sheet on top, smooth side up, and press gently.
- Cool, then refrigerate at least 6 hours or overnight.
Ice and cut
- Whisk the powdered sugar, milk and vanilla into a thick icing that spreads slowly. Spread it over the top pastry and let it set 20 minutes.
- Lift the slab out with the overhang. Cut into 9 slices with a serrated knife in short sawing strokes, wiping the blade between cuts.
Tips that make the difference
- Do not stop whisking while the custard cooks. Cornstarch catches on the bottom of the pan in seconds.
- If lumps form, whisk hard off the heat, or push the custard through a sieve before pouring it over the pastry.
- Pour the custard hot. It settles flat and bonds with the pastry; cooled custard goes on in lumps.
- Saw, do not press. Pressing straight down squeezes the custard out before anybody takes a bite.
Variations
- Pink icing. Add a drop of red food coloring to half the icing and feather it through the white, the way many British bakeries do.
- Passion fruit icing. In Australia a passion fruit icing is common: mix the pulp of 1 passion fruit into the powdered sugar instead of the milk.
- Lighter custard. Use all milk and no cream for a slightly firmer, less rich custard.
- Individual slices. Cut the baked pastry into rectangles first and pipe the custard between them for neater portions.
Storage and make-ahead
Keep the slices covered in the refrigerator for up to 2 days. After that the pastry softens from the custard.
The pastry sheets can be baked a day ahead and kept in an airtight tin. Assemble the slice the day before you want to serve it.
Custard slices do not freeze well; the custard weeps and the pastry turns soggy when thawed.
Frequently asked questions
How thick should the custard be?
Thick enough to fall from the whisk in heavy ribbons that hold their shape on the surface for a few seconds, and to bubble slowly like porridge. Then cook it one more minute.
Why did my custard not set?
It was not boiled long enough. Cornstarch needs to bubble for about a minute to thicken fully. It can also be a little short on cornstarch if measured by scooping; spoon it into the cup and level it.
Is a vanilla slice the same as a custard slice?
Yes. Different bakeries and regions use either name for the same pastry, custard and icing slice.
Can I use vanilla bean instead of extract?
Yes. Scrape the seeds of one bean into the milk as it heats and remove the pod before you whisk the milk into the yolks.
Make it the day before, chill it overnight, cut it with a serrated knife, and do not be surprised when the custard comes out the sides anyway. That is how you know it is right.
British Vanilla Custard Slice (Puff Pastry, Thick Set Custard, White Icing)
The British bakery custard slice, also called the vanilla slice: crisp flat puff pastry, a thick vanilla custard that stands up when cut, and white icing on top. US cups with grams, and how thick the custard must be.
Ingredients
- 1 package (about 17 ounces, 490g) frozen all-butter puff pastry, 2 sheets, thawed
- 3 cups whole milk
- 1 cup heavy cream
- 3/4 cup granulated sugar
- 2/3 cup cornstarch
- 6 large egg yolks
- 2 tablespoons unsalted butter
- 1 tablespoon vanilla extract, or the seeds of 1 vanilla bean
- Pinch of fine salt
- 1 1/2 cups powdered sugar
- 2 to 3 tablespoons milk
- 1/2 teaspoon vanilla extract
Instructions
- Heat the oven to 400 degrees (200°C). Line two baking sheets with parchment.
- Lay each pastry sheet on a lined baking sheet and prick all over with a fork. Cover with another sheet of parchment and set a second baking sheet on top to weigh it down.
- Bake for 20 minutes, then remove the top tray and parchment and bake 5 to 10 minutes more, until deep golden and crisp. Cool completely.
- Line an 8 inch square pan with plastic wrap or parchment, leaving an overhang. Trim both pastry sheets to fit the pan exactly. Lay one in the bottom, smooth side down.
- Heat the milk and cream in a saucepan until steaming.
- In a bowl, whisk the sugar, cornstarch, egg yolks and salt into a smooth thick paste. Slowly whisk in the hot milk.
- Pour everything back into the pan and cook over medium heat, whisking constantly and scraping the corners, until it thickens. Keep whisking until it bubbles slowly in the center, then cook a full minute more. It is thick enough when it falls from the whisk in heavy ribbons that hold their shape on the surface for a few seconds.
- Off the heat, whisk in the butter and vanilla. Pour the hot custard over the pastry in the pan and smooth it level. Lay the second pastry sheet on top, smooth side up, and press gently.
- Cool, then refrigerate at least 6 hours or overnight.
- Whisk the powdered sugar, milk and vanilla into a thick icing that spreads slowly. Spread it over the top pastry and let it set 20 minutes.
- Lift the slab out with the overhang. Cut into 9 slices with a serrated knife in short sawing strokes, wiping the blade between cuts.
