Make the Chocolate Cake:

1. Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper and lightly grease it.
2. In a bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
3. In another bowl, whisk granulated sugar, brown sugar, buttermilk, coffee, oil, eggs, and vanilla extract until smooth.
4. Gradually mix the wet ingredients into the dry ingredients until fully combined.
5. Pour batter into the prepared pan and smooth the top.
6. Bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean.
7. Let the cake cool completely before cutting.

Cut and Layer the Cakes:

8. Use a heart-shaped cookie cutter to cut out mini cake hearts from the cooled cake.
9. For each mini cake, stack two or three layers, spreading cream filling between each layer.

Make the Cream Filling:

10. In a chilled bowl, whip heavy cream, powdered sugar, and vanilla (or cocoa powder for chocolate filling) until stiff peaks form.
11. Pipe or spread the cream onto one cake layer, then place another layer on top. Repeat for multiple layers.

Decorate and Serve:

12. Dust with powdered sugar, top with berries, or sprinkle chocolate shavings.
13. Serve immediately or refrigerate until ready to enjoy!