In a small saucepan, combine fresh blackberries with granulated sugar and a splash of water over medium heat. Cook for about 10 minutes, stirring occasionally, until the mixture thickens. Strain and cool.

Preheat your oven to 350°F (175°C). Grease two 8-inch round cake pans and line the bottoms with parchment paper.

In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.

Beat the unsalted butter and granulated sugar together until light and fluffy, about 3-5 minutes.

Add eggs one at a time, mixing until incorporated, then add vanilla extract and lemon zest.

Mix buttermilk and cooled blackberry reduction in a separate bowl. Gradually add this to the butter mixture, alternating with dry ingredients.

Divide the batter between the prepared cake pans. Bake for 28-32 minutes, until a toothpick comes out clean. Cool in pans for 10 minutes before transferring to a wire rack.

Beat together cream cheese and softened butter until smooth. Gradually add powdered sugar and blackberry puree, beat until silky.

Once cooled, place one cake layer on a serving plate, spread frosting, layer second cake on top, and frost the top and sides. Decorate with fresh blackberries.