zest of 1 lemon
1/2 cup butter at room temperature
2 large eggs, at room temperature
1 tsp vanilla extract
1 3/4 cups all purpose flour
1/4 cup cornstarch
2 tsp baking powder
1 tsp salt
1/2 cup cultured buttermilk
2 cups fresh blueberries
Preheat oven to 350F.
Lightly grease and line a 9x9 inch square pan with parchment paper.
First make the lemon sugar. Put the sugar and lemon zest into a food processor and process until the zest is completely incorporated in to the sugar and it's pale yellow and fragrant. If you don't have a processor, just finely grate the zest and mix it into the sugar.
Cream the sugar and butter together until pale and fluffy, I like to go for a full 5 minutes, scraping down the bowl as necessary. I do this in a stand mixer.
Beat in the eggs, one at a time. Beat each one well, and scrape down that bowl. Blend in the vanilla.
Whisk together the flour, cornstarch, baking powder and salt.
Take about a tablespoon of the flour mixture and toss with the blueberries. Then add the rest to the mixer and blend until almost incorporated. Then blend in the buttermilk, just until everything is mixed, but don't over do it. Gently fold in the blueberries.
Spoon the dough (it will be thick) into the prepared pan and spread out evenly. Sprinkle some sparkling sugar over the surface if you're using. Bake for about 40 minutes, or until golden and a toothpick inserted in the center comes out without wet batter clinging to it. I like to loosely cover the cake toward the end of baking to keep it from browning too much.
