In a medium saucepan over medium heat, combine fresh blackberries, sugar, and a splash of water. Cook for about 10 minutes until the blackberries break down and thicken slightly. Strain the mixture and let it 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.

In a separate bowl, beat the unsalted butter and sugar together until light and fluffy, about 3-4 minutes. Add the eggs one at a time, mixing well after each addition.

On low speed, incorporate the pure vanilla extract and freshly grated lemon zest into the butter mixture.

Mix the cooled blackberry puree with the buttermilk until well combined. Gradually add to the butter mixture, beating slowly until cohesive.

Slowly add the dry ingredients to the wet mixture in three parts, alternating with the blackberry-buttermilk blend, mixing until just combined.

Divide the batter evenly between the prepared cake pans and smooth the tops.

Bake for 28-32 minutes until a toothpick comes out clean. Allow to cool in pans for 10 minutes before transferring to wire racks.

Make the frosting by beating cream cheese and butter together until creamy. Gradually add powdered sugar and reserved blackberry puree until smooth.

Once cakes are cooled, place one layer on a serving plate. Spread frosting on top, place the second layer, and frost the top and sides of the cake.