Preheat the oven to 350°F (175°C). Grease and line the bottom of three 9-inch cake pans with wax paper.
In a large mixing bowl, whisk together the flour, sugar, cocoa, baking soda, baking powder, and salt.
In a separate bowl, combine the buttermilk, oil, eggs, vanilla extract, almond extract, and bourbon.
With the mixer on low speed, slowly add the wet ingredients to the dry ingredients.
Add the hot coffee and mix until fully combined. Divide the batter evenly among the prepared pans.
Bake for 20-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool completely before frosting.
For the buttercream, place the egg whites and sugar in a heatproof bowl over simmering water. Whisk constantly until the sugar dissolves and the mixture reaches 160°F (70°C).
Transfer the bowl to a mixer and whisk on medium-high speed for about 5 minutes, until stiff peaks form.
Lower the speed and add the softened butter piece by piece until fully incorporated. If the mixture becomes soft, whisk again until stiff peaks form.
Slowly fold in the blackberry puree. Continue whisking until the buttercream is firm and fluffy.
Once the cakes have cooled, spread the blackberry buttercream between each layer and over the top and sides of the cake. Enjoy!