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

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 2 teaspoons of baking powder, and a pinch of salt.

In a separate bowl, beat 1 cup of softened butter and 1 ½ cups of granulated sugar until light and fluffy, about 4-5 minutes.

Add 4 eggs one at a time, incorporating each before adding the next. Blend in the zest of 2 lemons.

Gradually add the flour mixture to the wet ingredients, alternating with 1 cup of whole milk, mixing until just combined.

Divide the batter evenly among the three prepared pans. Bake for 25-30 minutes, or until a toothpick comes out clean.

Let the cakes cool in their pans for about 10 minutes, then transfer to wire racks to cool completely.

To prepare the buttercream, beat 1 cup of softened butter until creamy, then gradually add 4 cups of powdered sugar and 1 cup of blackberry puree and 2 tablespoons of lemon juice.

Assemble the cake by placing one layer on a serving plate, spreading blackberry buttercream on top, and repeating with the other layers.

Decorate the top with fresh blackberries and lemon slices. Chill for 30 minutes before slicing.