Pre-heat the oven to 400ºF, or pre-heat your air fryer to 330ºF.

Butter and sugar two 6-ounce ramekins. (Butter the ramekins and then coat the butter with sugar by shaking it around in the ramekin and dumping out any excess.)

Melt the chocolate and butter together, either in the microwave or in a double boiler. In a separate bowl, beat the egg yolks vigorously. Add the sugar and the vanilla extract and beat well again. Drizzle in the chocolate and butter, mixing well. Stir in the flour, combining until there are no lumps.

In a separate bowl, whisk the egg whites to soft peak stage (the point at which the whites can almost stand up on the end of your whisk). Fold the whipped egg whites into the chocolate mixture gently and in stages.

Transfer the batter carefully to the buttered ramekins, leaving about ½-inch at the top. (You may have a little extra batter, depending on how airy the batter is, so you might be able to squeeze out a third soufflé if you want to.) Place the ramekins on a baking sheet and transfer to the middle rack in the oven. Bake, without opening the door for 15 to 20 minutes. If you're using your air fryer, air-fry for 14 minutes at 330ºF. The soufflés should have risen nicely and be set through.

Dust with powdered sugar and serve immediately with heavy cream to pour over the top at the table.