Butter four 6-ounce ramekins, brushing the butter upward along the sides.

Coat the inside of each ramekin with granulated sugar and tap out the excess.

Place the ramekins on a baking sheet.

Melt the chopped chocolate and 2 tablespoons butter together until smooth. Let cool slightly.

Whisk the egg yolks, vanilla extract, and salt into the melted chocolate mixture.

In a clean bowl, beat the egg whites until foamy.

Add the cream of tartar and beat until soft peaks form.

Gradually add 1/4 cup sugar and beat until glossy medium-stiff peaks form.

Stir one-third of the whipped egg whites into the chocolate mixture to loosen it.

Gently fold in the remaining egg whites until no large white streaks remain.

Divide the batter evenly between the prepared ramekins.

Smooth the tops and run your thumb around the inside rim of each ramekin.

Bake for 12 to 14 minutes, or until puffed and set around the edges.

Dust with powdered sugar if desired and serve immediately.