- 1 1/2 cups semisweet chocolate chips
- 6 tablespoons butter
- 6 eggs, separated
- 1/2 cup white sugar
- Preheat oven to 275 degrees F (135 degrees C). Line 2 muffin tins with liners.
- Combine chocolate chips and butter in a saucepan over medium-low heat. Stir until melted and smooth, about 3 minutes. Remove from heat. Let cool slightly, about 5 minutes. Whisk in egg yolks.
- Beat egg whites in a large bowl with an electric mixer until soft peaks form. Gradually add sugar with mixer running, beating until peaks are stiff and glossy.
- Stir some of the egg whites into the chocolate mixture to lighten it. Pour chocolate mixture into the bowl of egg whites and fold until batter is well-mixed.
- Scoop batter into prepared muffin tin, filling each cup 3/4 of the way full.
- Bake in the preheated oven until cupcakes are just set in the center, about 25 minutes. Place muffin tin on a wire rack to cool, about 5 minutes. Remove cupcakes from the tin and let cool completely, about 15 minutes.