Lemon Sheet Cake

Ingredients

• 2 cups all-purpose flour
• 1/4 cup cornstarch
• 3/4 tsp baking powder
• 1/2 tsp baking soda
• 1/2 tsp salt
• 1 1/2 cups granulated sugar
• 2 Tbsp lemon zest
• 3/4 cup unsalted butter, softened
• 4 large eggs
• 1 tsp vanilla extract
• 1/2 cup buttermilk
• 1/2 cup sour cream
• 2 Tbsp fresh lemon juice
• 3 1/4 cups powdered sugar
• 1/3 cup fresh lemon juice
• Fresh strawberries, raspberries or blueberries for topping
• Sliced lemons and mint leaves, for decoration, optional

Directions

1. Heat the oven to 350 degrees. Butter an 18 by 13-inch rimmed baking sheet, your standard cookie sheet size, dust it with flour, and tap out the extra.
2. In a mixing bowl, combine the flour with the cornstarch, then whisk in the baking powder, baking soda, and salt for 20 seconds. Set that aside for the moment.
3. Set up a stand mixer with the paddle attachment. In the mixer bowl, beat the sugar with the lemon zest for 30 seconds, until the sugar smells lemony and has a pale yellow tint.
4. Add the butter and beat on medium speed until the mixture is very light and airy. Mix in the eggs 1 at a time, then blend in the vanilla extract.
5. In a bowl or a 2-cup liquid measuring cup, whisk the sour cream into the buttermilk, then whisk in the 2 Tbsp lemon juice. On low speed, blend 1/3 of the flour mixture into the butter mixture only until it is incorporated, then add 1/2 of the buttermilk mixture and mix just until it disappears.
6. Go through that same flour, then buttermilk, addition 1 more time; finish with the last 1/3 of the flour mixture and mix only until the batter comes together. Use a rubber spatula to sweep the sides and base of the bowl, then fold the batter over itself several times so everything is evenly mixed.
7. Transfer the batter to the prepared baking sheet and spread it level; it will look like a slim layer, but it should rise close to the rim. Bake for 22 – 25 minutes, until a toothpick pushed into the middle comes out clean. Set it on a wire rack and let it cool all the way.
8. For the glaze, whisk the powdered sugar with the lemon juice in a mixing bowl until no lumps remain. If the texture needs adjusting, use a little extra powdered sugar to make it thicker or a splash more lemon juice to loosen it.
9. Spread the glaze over the cooled cake. Chill for 20 minutes so the glaze can firm up a bit; it will not become completely set, but this pause gives you tidier slices. Right before serving, add the berries, lemon slices, and mint.