Circle B Kitchen
This recipe is so perfect as it is, but I did make a couple of changes to the topping by adding a bit more butter to give it better clumping properties. I also used very cold butter and processed it with the flour and sugar in a small food processor which saves a little time from working it in by hand. Either way works just fine though.
1 tablespoon unsalted butter, at room temperature, for pan (spray with nonstick cooking spray)
Crumb Topping
1/2 cup (2 1/2 ounces) all-purpose flour
1/3 cup (2 1/4 ounces) granulated sugar
1/8 teaspoon fine sea salt
Zest of 1 lemon
1/3 cup (2 ounces) unsalted butter (see headnote), at room temperature, cubed
Cake
1 1/2 cups plus 2 tablespoons (8 1/4 ounces) all-purpose flour
1 teaspoon baking powder
1/4 teaspoon baking soda
1/2 teaspoon fine sea salt
1/4 teaspoon freshly grated nutmeg
6 tablespoons (3 ounces) unsalted butter, at room temperature
3/4 cup (5 1/4 ounces) granulated sugar
Zest of 1 lemon
2 eggs
1/2 cup buttermilk
2 cups (10 ounces) blueberries, fresh or frozen
Lemon Syrup
1/3 cup (2 1/4 ounces) granulated sugar
Juice of 2 lemons
Preheat the oven to 350° F. Butter a 9-inch square baking pan.
To make the crumb topping, (see headnote) mix together the flour, sugar, salt, and lemon zest together in a bowl, then add the butter and use a fork or your fingers to cut the butter until the size of peas. Place the topping in the freezer while you mix the cake batter.
To make the cake, whisk the flour, baking powder, baking soda, salt, and nutmeg together in a bowl. Using a handheld mixer with beaters or a stand mixer with the paddle attachment, cream the butter, sugar, and lemon zest together on medium-high speed for 3 to 5 minutes, until light and fluffy. Add the eggs one at a time, scraping down the sides of the bowl after each addition. Stir in the flour mixture in three additions, alternating with the buttermilk in two additions, beginning and and ending with the dry ingredients and scraping down the sides of the bowl occasionally. Gently fold in 1 cup of the blueberries, spread the batter into the prepared pan, and distribute the remaining 1 cup of blueberries over the cake.
Sprinkle the chilled crumb topping over the berries, then bake for 45 to 50 minutes, or until lightly golden and firm on top.
To make the glaze, combine the sugar and lemon juice in a small saucepan and whisk until blended. Cook over medium-low heat, stirring occasionally, for 8 to 10 minutes, until syrupy. The glaze will bubble while cooking, so you may need to remove it from the heat to check that it is thick enough.
Pour the glaze over the cake as soon as it is removed from the oven. Reheat the syrup briefly if it has become too thick to pour.
Storage: Covered in plastic wrap, the buckle will keep at room temperature for 2 to 3 days.