Chocolate Soufflé Cake

Preparation

1. Step 1

   Heat oven to 350 degrees. Butter a 9-inch springform pan and line the bottom with parchment paper.

2. Step 2

   In a large heat-safe bowl set over a pot of simmering water, or in a microwave, melt the butter and chocolate together; stir until smooth.

3. Step 3

   Add ¼ cup/50 grams of the sugar to the bowl of a stand mixer fitted with the whisk attachment. Separate 4 of the eggs and add the yolks and remaining whole egg to the sugar in the stand mixer bowl. (Alternatively, you can use a large bowl and handheld electric mixer.) Beat on medium-high speed until light in color, foamy and about doubled in volume, about 5 minutes. The egg mixture should fall from the whisk in ribbons.

4. Step 4

   Add the egg mixture to the melted chocolate mixture. Add the rum (if using), vanilla, espresso powder (if using) and salt; fold gently until combined and no streaks remain.

5. Step 5

   Wash and dry the mixer bowl, add the remaining egg whites and beat on medium-high until foamy. Slowly add the remaining ¾ cup/150 grams sugar, about 1 tablespoon at a time, and beat until soft peaks form, about 4 minutes.

6. Step 6

   Add about 1 cup of the egg white mixture to the chocolate mixture and fold until well combined. Add the remaining egg white mixture and fold gently until well combined. Transfer the batter to the pan and smooth the top.

7. Step 7

   Bake the cake until puffed slightly over the edge of the pan and the edges are set but the center is still wobbly, 25 to 30 minutes.

8. Step 8

   Let the cake cool in the pan set on a wire rack for about 30 minutes, until room temperature or just a tiny bit warm. Carefully run a thin knife or offset spatula around the sides of the pan, then remove the ring. Dust with cocoa powder and serve at room temperature or just slightly warm, with whipped cream or ice cream. Use a warm, clean, dry knife for the tidiest slices. Loosely cover any leftover cake and store in the refrigerator for up to 3 days.