Madeleine's Chocolate Souffle

Preheat oven to 350 degrees with rack positioned on bottom. Butter a 6-cup souffle mold (7 1/2-by-7 1/2-by-3 1/4 inches), then sprinkle sides and bottom of mold with 1 1/2 tablespoons sugar.

Melt both types of chocolate together in a metal bowl set over a pan of simmering water. Remove the chocolate from the heat; transfer to a large bowl. Let cool until an instant-read thermometer registers 114 degrees.

In the bowl of an electric mixer fitted with the whisk attachment, beat egg yolks, the remaining 1/2 cup sugar, and the salt until mixture is thick and light yellow. Alternatively, use a hand whisk.

Mix the cooled chocolate, heavy cream, espresso powder, and liquor into the yolk mixture until well blended and smooth.

In a separate bowl, beat egg whites until stiff peaks form, being careful not to overbeat. Mix one-quarter of the egg whites into the chocolate-egg yolk mixture. Gently fold in the remaining egg whites until well blended. Pour the mixture into the prepared souffle mold.

Bake the souffle until center has just barely set, 14 to 16 minutes. Serve immediately.