Blueberry Cornmeal Butter Cake

8 tablespoons (115 grams or 1 stick) unsalted butter, at room temperature, plus more for pan
1 cup (125 grams) all-purpose flour, plus more for pan
½ cup (60 grams) cornmeal
2 teaspoons baking powder
½ teaspoon table salt
1 cup (200 grams) sugar
2 large eggs
¼ teaspoon vanilla extract
¼ teaspoon freshly grated lemon zest
⅓ cup (80 grams) sour cream
2 cups (190 grams) blueberries, rinsed and patted dry

Streusel:

It’s that kind of cake—dense and buttery, dotted with dreamy berries, portable, quick to make, and infinitely snacky.

Preheat your oven to 350 degrees. Line the bottom of an 8-inch square pan with parchment, then either butter and flour the bottom and sides, or coat them with a nonstick spray.
Whisk the flour, cornmeal, baking powder, and salt in medium bowl, and set aside. Using an electric mixer, beat the butter with sugar in large bowl until pale and fluffy, for at least 2 minutes. Beat in the eggs one at a time, scraping down the bowl between additions, then add the vanilla and zest. Add a third of flour mixture, all of sour cream, and another third of the flour, beating until just blended after each addition. Scrape down sides of bowl. Mix the remaining third of the flour mixture with the blueberries. Fold the blueberry-flour mixture gently into the cake batter.
Spread the cake batter in the prepared cake pan. Use your original dry-ingredients bowl (see how we look out for your dishpan hands?) to combine the dry topping ingredients with a fork. Mash in the butter with your fork, fingertips, or a pastry blender. Scatter the topping over the batter.
Bake the cake until the top is golden brown and the tester inserted into center comes out clean, about 35 minutes. Cool the cake in the pan on a rack for 5 minutes. Run the spatula around the edges of the cake to loosen it, then flip out onto a cooling rack.