Preheat oven to 400 degrees F. Butter a 2 quart souffle dish or 6 8 ounce ramekins. Sprinkle with about 1/4 cup sugar. Combine espresso and chocolate in a small bowl and microwave about a minute; stir to combine and melt chocolate. Whisk egg yolks into chocolate.
Beat egg whites until frothy. Gradually add 1/4 cup sugar and continue beating until soft peaks form. Stir about 1 cup of the egg whites into chocolate, then fold remaining egg whites into chocolate.
Spoon into prepared dish(es) so they are about 3/4 full. Bake 30 to 40 minutes for large souffle; 20 to 25 minutes for individuals. Once souffle has risen, remove from oven and serve.