Dark Chocolate Souffle Cake

Dark Chocolate Souffle Cake
from Fresh Everyday by Sara Foster

Ingredients:
8 tablespoons unsalted butter, cold, cut into 1-inch pieces, plus more for buttering the pan
1/2 cup sugar, plus more for dusting the pan
8 ounces bittersweet chocolate, chopped
2 tablespoons coffee liqueur, I used Starbucks
1 teaspoon vanilla extract
1 teaspoon ground cinnamon
6 large eggs, separated

Directions:
1. Preheat the oven to 350ºF. Butter a 9-inch springform pan and dust lightly with sugar.
2. Melt the butter and chocolate together in a heavy-bottomed saucepan over low heat, stirring constantly. Remove from the heat; stir in the coffee liqueur, vanilla, and cinnamon, and set aside to cool to room temperature.
3. Beat the egg yolks and sugar together in a medium bowl with an electric mixer on high speed until pale yellow and thick enough to hold a ribbon, about 3 minutes. The ribbons will remain visible when you lift up the beater. Gently fold a quarter of the beaten eggs into the chocolate mixture. Pour the chocolate with the added eggs into the bowl with the remaining eggs and fold gently to combine.
4. In a separate large bowl, beat the egg whites to soft peaks. Fold a quarter of the egg whites into the chocolate batter to lighten it, then gently fold in the remaining whites until incorporated. Do not over-mix the batter; better that you still see little traces of the egg whites that you overwork the batter and end up with a leaden cake.
5. Pour the batter into the prepared pan and smooth it with a rubber spatula to make even. Bake on a center rack for 30 to 35 minutes, until the edges of the cake are set but the center is still soft. It will set completely as it cools. Cool the cake on a wire rack for about 5 minutes. Run a knife around the edge to loosen the cake. Open the springform pan to release the sides and transfer the cake onto a serving plate. Slice and serve immediately.