Position rack in center of oven; preheat to 375 degrees F. Lightly coat two 10-ounce ramekins with cooking spray; coat the insides of each with 1 1/2 teaspoons sugar.

Place chocolate in a small microwave-safe bowl. Microwave on Medium, stirring every 20 seconds, until melted, 1 to 2 minutes. (Alternatively, see "No Microwave?" below.)

Whisk egg yolk and cream in a medium bowl until combined. Whisk in the chocolate until smooth, then whisk in flour and cinnamon until incorporated.

Beat egg whites and salt in a medium bowl with an electric mixer on high speed until soft peaks form. Beat in the remaining 2 tablespoons sugar in four additions, until stiff, glossy peaks form.

Using a rubber spatula, gently fold half the beaten whites into the chocolate mixture until fairly smooth; then gently fold this combined mixture back into the remaining egg whites until no white streaks remain. Divide between the prepared ramekins and place on a baking sheet. Bake until puffed and firm to the touch, 18 to 22 minutes. Dust with confectioners' sugar, if desired. Serve immediately.

No Microwave? Place chopped chocolate in the top of a double boiler over hot, but not boiling water. Gently stir until almost melted. Remove from the heat and stir until the chocolate melts completely.

MAKE AHEAD TIP: Equipment: Two 10-ounce ramekins