Prepare Blackberry Reduction: In a saucepan, combine fresh blackberries, sugar, and a splash of water. Cook over medium heat for 10 minutes, until thickened. Strain and cool.

Preheat Oven: Heat your oven to 350°F (175°C). Prepare two 8-inch round cake pans by greasing and lining with parchment.

Mix Dry Ingredients: In a bowl, whisk together flour, baking powder, baking soda, and salt.

Cream Butter and Sugar: Beat butter and sugar together until light and fluffy.

Incorporate Eggs: Add eggs one at a time, mixing on low speed until fully incorporated.

Combine Wet Ingredients: Whisk buttermilk and cooled blackberry reduction together.

Combine Dry and Wet Mixtures: Gradually add dry ingredients to wet ingredients, alternating with blackberry mixture.

Bake: Divide batter between pans and bake for 28-32 minutes, until a toothpick comes out clean.

Cool Cakes: Cool in pans for 10 minutes, then invert onto a wire rack to cool completely.

Make Frosting: Beat butter and cream cheese until smooth, add powdered sugar and blackberry reduction until fluffy.

Assemble Cake: Frost the first layer, add the second layer, and frost top and sides.