If baking right away, position a rack in the lower third of the oven & heat to 375°.

Grease ramekins & sprinkle with sugar.

Put chocolate, butter, and milk in a heatproof bowl over a pot of barely simmering water. Stir until chocolate is melted & mixture is smooth.

Remove the bowl & whisk in the egg yolks. (Don’t worry if the mixture isn’t perfectly smooth at this point.)

In a medium bowl beat egg whites & cream of tartar with an electric mixer on medium speed until soft peaks form. Gradually sprinkle in a 1/4 cup sugar and beat on high until the whites are stiff peaks.

Fold 1/4 of the egg whites into the chocolate mixture to lighten it then gently fold in the remaining egg white until just incorporated.

Divide mixture evenly among the prepared ramekins, filling each 3/4 full. The soufflés can be prepared to this point, covered tightly, and refrigerated up to 2 days or frozen for up to a few months. Bake directly from the refrigerator or freezer (do not thaw if frozen).

Put soufflés on a baking sheet. Bake until they rise & crack on top and a wooden skewer in the center emerges gooey (but not completely liquid), 14-16 minutes (15-17 from fridge, 17-20 if from freezer). Dust with a bit of powdered sugar, and maybe an extra dash of cayenne and salt if you like. Serve immediately.