6tablespoons(85 g) unsalted butter, room temperature and cubed
Cake
2cups(250 g) all purpose flour
1 ½teaspoonsbaking powder
½teaspoonbaking soda
½teaspoonsalt
½cup(113 g) unsalted butter, room temperature
1cup(200 g) granulated sugar
2large eggs, room temperature
2teaspoonspure vanilla extract
1cup(240 g) full-fat sour cream, room temperature
1 ½cupsfresh blueberries, (or frozen blueberries)
1Tablespoonfresh lemon zest, (from one lemon)
Vanilla Glaze
½cup(60 g) confectioners' sugar, sifted
½teaspoonpure vanilla extract
1Tablespoonmilk
Instructions
Preheat oven to 350° F. Grease a 9-inch springform baking pan with butter and set aside.
Streusel
In a small bowl, whisk together flour, brown sugar, cinnamon and salt. Cut the butter into the mixture using a pastry blender (or your hands) until the mixture forms coarse crumbs and resembles sand. It will seem dry at first, but keep working in the butter and it will come together. Place bowl in the refrigerator to keep cold while you prepare the batter.
Cake
In a medium bowl, whisk together flour, baking powder, baking soda and salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat butter and sugar together until light and fluffy, about 2 minutes.
Add eggs one at a time, beating well after each addition. Add vanilla and lemon zest, then mix just until combined. Scrape down the sides and bottom of the bowl as necessary.
With the mixer on low, add half of the flour mixture and mix just until combined. Add the sour cream and mix until incorporated. Add remaining flour mixture and mix just until combined. Fold in the blueberries.
Assembly
Pour the batter into prepared pan. Use an off-set spatula or knife to spread evenly across the bottom of the pan. Sprinkle the streusel mixture evenly over the top.
Bake at 350° F for 55 to 60 minutes or until a toothpick inserted in the center comes out with little to no crumbs. Allow cake to cool for 10 minutes, then run a butterknife around the edge and release the sides of the pan. As the cake cools, the center will fall or "buckle," hence the name!
Vanilla Glaze
In a small bowl, whisk together confectioners' sugar, vanilla and milk. Use a spoon to drizzle glaze over blueberry buckle. Cut and serve with coffee. Enjoy!
Notes
Frozen blueberries: Do not defrost. Toss in 1 Tablespoon flour before folding into the batter.Sour cream: Full fat will provide the best flavor and texture. Plain yogurt works well too.Glaze: To make a lemon glaze, whisk together 1/2 cup confectioners' sugar with 1 Tablespoon fresh lemon juice.Store at room temperature for 3 days or in the refrigerator for 1 week.Freeze after the cake has cooled completely. Wrap in plastic wrap and aluminum foil to prevent freezer burn. Defrost in the refrigerator before bringing to room temperature and serving.Baking pans: A 9-inch square pan or 10-cup bundt pan may also be used. Baking time will be closer to 45 minutes.