Chocolate Heart-Shaped Cakes with Buttercream

1. Preheat oven to 300°F. Spray the hollows of a 5-cup heart-shaped nonstick cake pan or an 8-cup silicone mold with cooking spray (see cook's note for product links). If not using silicone mold, line bottoms with parchment.

2. In a medium heatproof bowl, dissolve espresso in hot water. Add chocolate and rum and place over (but not in) a pot of simmering water. Stir until chocolate has melted and mixture is smooth. Remove from heat; let cool slightly.

3. In a heatproof bowl, combine eggs and granulated sugar. Place over (but not in) pot of simmering water and whisk until sugar has dissolved and mixture is warm to the touch. Transfer to a mixer fitted with the whisk attachment and beat on medium-high speed until mixture is thick, fluffy, and almost doubled in volume, about 3 minutes (or, if not using a stand mixer, you can beat with a hand mixer directly over the heat).

4. Whisk cream with confectioners' sugar and vanilla until soft peaks form. Fold chocolate mixture into egg mixture, then gently but thoroughly fold in whipped cream.

5. Divide mixture among hollows of prepared pan (about 1/2 cup per hollow for 5-cup; about 1/3 cup for 8-cup). Place filled pan in a large roasting pan on middle rack of oven. Add boiling water to roasting pan to come halfway up sides of cake pan. Bake until a tester inserted in centers comes out clean, 40 to 50 minutes.

6. Remove from oven and let cool completely in water bath. Remove from water, cover, and refrigerate at least 4 hours and up to 24 hours. Just before serving, dip bottom of pan in warm water to loosen, about 1 minute. Run a small offset spatula around edges of cakes, then lift each out of pan; or cover with a platter and invert to remove. Remove parchment (if using). Use a pastry bag fitted with desired tip (Martha used a variety of star and leaf tips) to pipe buttercream or whipped cream onto cakes. Serve immediately.

Cook's Notes

We like the Fox Run Linked Heart four-inch pan, and the Bakerpan eight-cavity silicone mini-cake pan, both available at Amazon.com. Martha used a pastry bag fitted with small leaf and star tips to decorate the tops of her chocolate cakes with the Swiss-meringue buttercream.