Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans (or line with parchment). In a medium bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.

In a large bowl, beat the softened butter and sugar together until light and fluffy. Add the eggs one at a time, mixing well after each. Stir in the vanilla, lemon zest, and lemon juice. Alternately add the dry ingredients and buttermilk to the butter mixture, beginning and ending with the flour. Mix just until combined.

Divide batter evenly between the pans. Bake for 25–30 minutes or until a toothpick comes out clean. Let cool in pans for 10 minutes, then transfer to wire racks to cool completely

Beat the cream cheese, powdered sugar, lemon zest, and lemon juice together until smooth. In a separate bowl, whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the lemon cream cheese mixture until fully combined

If using frozen blueberries, toss them with 1 tablespoon flour to prevent bleeding. If using fresh, no flour needed. Fold the blueberries gently into the lemon crème.

Place one cake layer on a serving plate. Spread half of the lemon crème mixture over the top. Add the second cake layer and spread the remaining crème on top. Garnish with whipped cream, fresh blueberries, lemon slices, or a dusting of powdered sugar.

Refrigerate the assembled cake for at least 1 hour before serving to allow it to set. Slice and serve chilled.