Preheat the oven to 350°F (175°C) and prepare the cake pans.
In a large mixing bowl, cream together the softened butter and sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Mix in the vanilla extract and blackberry puree, combining thoroughly.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with the milk.
Divide the batter evenly into the prepared pans and smooth the tops.
Bake for 25-30 minutes or until a toothpick inserted comes out clean.
Allow cakes to cool in the pans for 10 minutes before transferring to a wire rack.
For the frosting, beat together the softened cream cheese and powdered sugar until smooth.
Add the blackberry puree gradually and continue mixing until combined.
Once the cakes are completely cool, place one layer on a serving plate and spread a layer of frosting on top.
Stack the second layer on top and frost the top and sides of the cake.
Decorate with fresh blackberries and optional edible flowers, if desired.