Step 1

To make the cake, preheat an oven to 350°F (180°C). Grease an 8-inch (20-cm) round cake pan and an 8-inch (20-cm) square cake pan, line the bottoms of the pans with parchment paper, then grease the parchment. Dust with flour, then tap out any excess.

Step 2

In a bowl, sift together the flour, cocoa powder, baking powder, baking soda and salt. Set aside.

Step 3

In the bowl of a stand mixer fitted with the flat beater, beat together the sugar, eggs, buttermilk, oil and vanilla on medium speed until blended, about 2 minutes. Reduce the speed to low, slowly add the flour mixture and beat until incorporated, stopping the mixer to scrape down the sides of the bowl as needed. Add the melted chocolate and espresso powder and beat until combined. Raise the speed to high and beat for 30 seconds.

Step 4

Divide the batter evenly between the prepared pans and spread evenly. Bake until a toothpick inserted into the center of the cakes comes out clean, 30 to 35 minutes. Transfer the pans to wire racks and let cool for 10 minutes, then invert the cakes onto the racks and let cool completely.

Step 5

To make the frosting, in the bowl of a stand mixer fitted with the flat beater, beat the butter on medium speed until smooth, about 2 minutes. Add the confectioners’ sugar, vanilla, and salt, raise the speed to medium-high, and beat until combined, stopping the mixer to scrape down the sides of the bowl as needed. Stir in the red food coloring, 1 drop at a time and stirring after each addition, until the frosting reaches your desired color.

Step 6

To assemble, cut the round cake in half crosswise. Orient the square cake as a diamond. Frost the cut sides of the half rounds with the frosting and place them against the top sides of the diamond to form a heart shape, pressing gently to adhere. Spread the remaining buttercream or frosting over the entire surface of the cake. Decorate as desired with edible flowers and serve. Serves 12 to 16.

Step 7

Adapted from Williams Sonoma Favorite Cakes (Weldon Owen, 2017)