Lightly coat eight 4- to 6-ounce ramekins with nonstick cooking spray. In a small bowl stir together the 2 tablespoons granulated sugar and the espresso powder. Sprinkle on the side and bottom of each dish. Place in a shallow baking pan; set aside.
In a medium saucepan stir together 1/2 cup of the granulated sugar, the cocoa powder, flour, and salt. Gradually stir in milk. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir for 1 minute more. Remove from heat. Slightly beat egg yolks. Slowly add chocolate mixture to egg yolks, stirring constantly.
In a large mixing bowl combine egg whites, vanilla, and cream of tartar. Beat with an electric mixer on high speed until soft peaks form (tips curl). Gradually add remaining 1/4 cup granulated sugar, beating on high speed until stiff peaks form (tips stand straight). Gently fold chocolate mixture into egg whites. Spoon into prepared dishes.
Bake in a 350 degrees oven about 25 minutes or until a knife inserted near centers comes out clean. If desired, sprinkle with powdered sugar. Serve immediately.