Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Then, line the bottoms with parchment for easy release.

In a small bowl, mash 1 1/2 cups of blackberries with a fork until juicy but still slightly chunky. Set aside.

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

In a large bowl, cream the butter and granulated sugar until light and fluffy. Add the eggs one at a time, beating well after each addition.

Mix in vanilla extract, lemon zest (if using), and purple food coloring (if desired).

Alternately add dry ingredients and buttermilk to the butter mixture, beginning and ending with dry ingredients. Mix just until combined.

Gently fold in mashed blackberries.

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

Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.

Reduce 1 cup of fresh blackberries to a thick puree over low heat, then strain to remove seeds.

In a large bowl, beat butter and cream cheese until smooth. Gradually add powdered sugar until frosty and fluffy.

Mix in blackberry puree, vanilla extract, and salt until smooth.

Place one cake layer on a serving platter and spread a layer of frosting over the top.

Add the second cake layer and cover the entire cake with the remaining frosting.

Garnish with extra blackberries, edible flowers, and mint leaves if desired.