Preheat your oven to 350 degrees. Lightly butter or spray a 9-by-13-inch baking dish with non-stick cooking spray. If using butter dust with a little flour and then tap out the pan. You can also line the bottom with parchment paper if you like easier cleanup.

In a medium bowl, sift together the 2 cups of all-purpose flour, the baking powder, baking soda, and salt. The sifting it ensures the dry ingredients are evenly combined with no lumps.

In a large bowl (or in the bowl of a stand mixer), beat together the butter, granulated sugar, and lemon zest on high speed until light in color and texture, about 3 minutes. You want it fluffy. Gradually beat in the eggs and then the vanilla extract. Reduce the speed to low and add the flour mixture in 3 additions, alternating with the sour cream, beginning and ending with the flour. Beat until smooth, stopping to scrape down the sides of the bowl as needed.

In a separate bowl, toss the fresh blueberries with the brown sugar, cinnamon, and the remaining 1 tablespoon of flour.

Spread half of the cake batter in the prepared pan. Scatter the blueberry mixture over the batter, taking care that no berries touch the sides of the pan. Spread the remaining batter over the berries, smoothing the top as evenly as you can.

To make the pecan streusel, combine the flour, brown sugar, and butter in a small bowl. Using your fingers, work the ingredients together until just combined, then work in the pecans. Press the mixture together into a ball and then separate it with your fingers into coarse crumbs. Sprinkle the streusel evenly over the top of the cake.

Bake until a toothpick inserted into the center of the cake comes out clean, about 45 minutes. Transfer the pan to a wire rack and let the cake cool in the pan for 15 minutes before cutting into squares.