In a small saucepan, combine 1 1/2 cups fresh blackberries with 2 tablespoons of sugar and a splash of water. Cook over medium heat for 8-10 minutes until thickened. Mash gently and strain through a fine mesh sieve to remove seeds. Cool completely. Set aside 1/2 cup for the cake and 1/3 cup for the frosting.

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

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large bowl or stand mixer, beat the butter and sugar on medium speed until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract and lemon zest (if using).

In a separate bowl, whisk together the buttermilk and the 1/2 cup cooled blackberry puree.

With the mixer on low, add the flour mixture to the butter mixture in three additions, alternating with the buttermilk-blackberry mixture. Begin and end with the dry ingredients. Mix just until combined. Add purple food coloring if desired.

Divide the batter evenly between the prepared pans. Smooth the tops and bake for 28-32 minutes, or until a toothpick inserted into the center comes out clean. Cool the cakes in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.

Beat the butter and cream cheese until smooth and fluffy, about 2 minutes. Gradually add the powdered sugar, blackberry puree (reduced to 1/3 cup), vanilla, and a pinch of salt. Beat until light and creamy, about 3 more minutes. Chill if it’s too soft.

Place one cake layer on a serving plate. Spread a generous layer of frosting on top. Add the second layer, then frost the top and sides. Decorate with fresh blackberries, edible flowers, or mint leaves.