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Blueberry buckle got its name from the cake itself. The crumb topping is so heavy that the cake rises in the oven, the crumb pushes it back down, and the whole top buckles and sinks in uneven waves. That is not a mistake, it is the point of it. A good buckle comes out of the oven lumpy, cracked and a little sunken in the middle, with blueberry juice bleeding purple up through the cracks. It is one of the oldest American pan cakes, part coffee cake and part fruit dessert, and it belongs on the table on a weekday morning with a cup of coffee.
Two things go wrong with it at home. The blueberries all sink to the bottom and make a wet purple layer under a plain cake, or the crumb melts into a flat sugary crust instead of staying in crunchy clumps. Both have simple answers. The batter has to be thick, almost stiff, so it holds the berries in place. The berries get a light coat of flour. And the crumb is made with cold butter and chilled before it goes on, so it bakes into crisp, craggy pieces. Here is how to keep the blueberries from sinking and the crumb crunchy.
Why this blueberry buckle works
- A thick, stiff batter. Less milk than an ordinary cake makes a batter that holds the berries up instead of letting them fall through.
- Floured berries. A light coat of flour gives each berry something to grip in the batter.
- Frozen berries kept frozen. If you use frozen blueberries, they go in straight from the freezer so they do not bleed and stain the whole cake.
- A cold crumb. Cold butter rubbed into the flour and sugar, then chilled, bakes into crunchy clumps instead of melting flat.
- A generous amount of crumb. The weight of the topping is what makes the buckle, so do not hold back.
Ingredients
Makes one 8 inch square cake, 9 generous squares. The measurements are in US cups with grams in brackets.
For the crumb topping
- 2/3 cup all-purpose flour (85g)
- 1/2 cup granulated sugar (100g)
- 1 teaspoon ground cinnamon
- A pinch of fine salt
- 6 tablespoons cold unsalted butter (85g), cut in small cubes
For the cake
- 2 cups all-purpose flour (250g), plus 1 tablespoon for the berries
- 2 teaspoons baking powder
- 1/2 teaspoon fine salt
- 1/2 cup unsalted butter (113g), softened
- 3/4 cup granulated sugar (150g)
- 1 large egg, at room temperature
- 1 teaspoon vanilla extract
- 1/2 cup whole milk (120ml)
- 2 1/2 cups blueberries (about 375g), fresh or frozen
Fresh or frozen blueberries both work. Wild frozen blueberries are small and spread evenly through the cake. Do not thaw frozen berries.
How to make blueberry buckle
Make the crumb
- In a bowl, mix the flour, sugar, cinnamon and salt. Add the cold butter and rub it in with your fingertips until the mixture holds together in clumps the size of peas and marbles when you squeeze it.
- Put the bowl of crumb in the refrigerator while you make the cake.
Make the cake
- Heat the oven to 350 degrees (175°C). Butter an 8 inch square metal pan and line the bottom with a strip of parchment that hangs over two sides.
- Whisk the 2 cups of flour, baking powder and salt together in a bowl.
- In a large bowl, beat the soft butter and sugar for 2 to 3 minutes, until pale and fluffy. Beat in the egg and the vanilla.
- Add the flour mixture in three parts, alternating with the milk in two parts, mixing on low just until no dry flour shows. The batter will be thick.
- Toss the blueberries with the extra tablespoon of flour in a separate bowl, then fold them into the batter with a spatula in a few strokes.
- Spread the batter in the pan and level it roughly. Scatter all of the cold crumb over the top in an even, heavy layer, pressing nothing down.
- Bake for 45 to 55 minutes, until the crumb is golden, the cake has buckled in places and a toothpick in the center comes out with moist crumbs but no wet batter.
- Cool in the pan for at least 20 minutes before cutting, so the berries set.
Tips that make the difference
- If the batter seems too thick to spread, that is right. A loose batter is the reason berries sink.
- Do not stir the berries in hard. Fold gently so they stay whole and do not streak the batter purple.
- Chill the crumb. Warm crumb melts into the cake; cold crumb stays in crunchy clumps.
- Bake in a metal pan. Glass heats slowly and the middle can stay wet under all that topping.
- Cut with a sharp knife wiped between cuts for clean squares.
Variations
- Lemon buckle. Add the finely grated zest of one lemon to the butter and sugar.
- Mixed berry. Use half blueberries and half raspberries or chopped strawberries.
- Peach buckle. Swap the blueberries for 2 1/2 cups of diced peaches, well drained.
- Pecan crumb. Stir 1/3 cup of chopped pecans into the crumb.
Storage and make-ahead
Keep the buckle covered loosely at room temperature for up to 2 days. Covering it tightly softens the crumb.
Refrigerate leftovers after that for up to 5 days, and warm a square for a few seconds before serving.
To freeze, wrap single squares well and freeze for up to 2 months. Thaw at room temperature.
Frequently asked questions
What is the difference between a buckle, a cobbler and a crumble?
A buckle is a cake with the fruit mixed into the batter and a crumb on top. A cobbler has a biscuit or batter topping over fruit, and a crumble is fruit under a crumb with no cake at all.
Why did my blueberries sink?
The batter was too thin, or the berries were not floured. Keep the batter thick and toss the berries in flour first.
Why did my crumb melt into the cake?
The butter was too soft. Use cold butter, rub it in only until it clumps, and chill the crumb before it goes on.
Can I use frozen blueberries?
Yes. Do not thaw them. Toss them in flour and fold them in straight from the freezer, and add a few minutes to the baking time.
Cut the first square while it is still a little warm, and let the sunken, cracked top tell you it is right.
Old-Fashioned Blueberry Buckle (Berries All Through, Crunchy Crumb Top)
An old-fashioned blueberry buckle: a thick butter cake packed with blueberries under a heavy cinnamon crumb that makes the cake buckle as it bakes, with berries that stay suspended and a topping that stays crunchy.
Ingredients
- 2/3 cup all-purpose flour
- 1/2 cup granulated sugar
- 1 teaspoon ground cinnamon
- A pinch of fine salt
- 6 tablespoons cold unsalted butter (85g), cut in small cubes
- 2 cups all-purpose flour (250g), plus 1 tablespoon for the berries
- 2 teaspoons baking powder
- 1/2 teaspoon fine salt
- 1/2 cup unsalted butter (113g), softened
- 3/4 cup granulated sugar
- 1 large egg, at room temperature
- 1 teaspoon vanilla extract
- 1/2 cup whole milk
- 2 1/2 cups blueberries (about 375g), fresh or frozen
Instructions
- In a bowl, mix the flour, sugar, cinnamon and salt. Add the cold butter and rub it in with your fingertips until the mixture holds together in clumps the size of peas and marbles when you squeeze it.
- Put the bowl of crumb in the refrigerator while you make the cake.
- Heat the oven to 350 degrees (175°C). Butter an 8 inch square metal pan and line the bottom with a strip of parchment that hangs over two sides.
- Whisk the 2 cups of flour, baking powder and salt together in a bowl.
- In a large bowl, beat the soft butter and sugar for 2 to 3 minutes, until pale and fluffy. Beat in the egg and the vanilla.
- Add the flour mixture in three parts, alternating with the milk in two parts, mixing on low just until no dry flour shows. The batter will be thick.
- Toss the blueberries with the extra tablespoon of flour in a separate bowl, then fold them into the batter with a spatula in a few strokes.
- Spread the batter in the pan and level it roughly. Scatter all of the cold crumb over the top in an even, heavy layer, pressing nothing down.
- Bake for 45 to 55 minutes, until the crumb is golden, the cake has buckled in places and a toothpick in the center comes out with moist crumbs but no wet batter.
- Cool in the pan for at least 20 minutes before cutting, so the berries set.
