1-First Step: Prep and mise en place Preheat the oven to 350°F and grease an 8×8-inch square pan, or line it with parchment paper for easy removal. Gather all ingredients so you can work quickly: measure the flour, sugars, butter, milk, egg, baking powder, salt, lemon zest, and blueberries. Rinse and pat dry the blueberries. Toss the 1 tablespoon of flour with the 1 1/2 cups fresh blueberries; this helps keep the berries suspended in the batter and reduces bleeding.

2-Second Step: Make the cake batter In a medium bowl, cream 3/4 cup granulated sugar and 1/4 cup softened butter until light and slightly fluffy. Beat in 1 egg and 2 teaspoons lemon zest until well combined. In a separate bowl, whisk 1 1/2 cups all-purpose flour with 2 teaspoons baking powder and 1/2 teaspoon salt. Add the dry mix to the butter mixture in two additions, alternating with 1/2 cup milk, starting and ending with the dry mix. Mix gently until just combined; overmixing can make the cake dense.

3-Third Step: Fold in blueberries and assemble Gently fold the floured blueberries into the batter. Pour the batter into the prepared 8×8-inch pan and smooth the surface with a spatula. The batter will be fairly thick and will cradle the berries as it bakes.

4-Fourth Step: Make the streusel topping Combine 1/3 cup all-purpose flour, 1/4 cup brown sugar, 1/4 cup granulated sugar, and 1/2 teaspoon cinnamon in a small bowl. Cut in 1/4 cup cold butter and 1 tablespoon cold butter until the mixture resembles coarse crumbs. Scatter the streusel evenly over the batter, pressing lightly so it adheres to the surface.

5-Fifth Step: Bake and test for doneness Bake the lemon blueberry buckle at 350°F for 45-50 minutes in the center of the oven. Start checking at 40 minutes: a toothpick inserted into the center should come out with a few moist crumbs but not wet batter. If using frozen blueberries, add 5-10 minutes to baking time. If making muffins, see the muffin conversion table below.

6-Final Step: Cool and serve Let the buckle cool in the pan on a wire rack for about 15-20 minutes, then run a knife around the edges and lift it out using the parchment. Cool another 20 minutes before slicing for cleaner pieces, or serve warm with whipped cream or yogurt. This lemon blueberry buckle serves 8-10 from an 8×8-inch pan.