My mother used to make individual chocolate cakes for me and my playmates. Each having our own made us feel extra special. Years later, I dusted off her recipe to prepare for old friends, adding a peanut butter center for a sweet-salty twist. — Marisa Churchill, Sweet and Skinny
Preheat the oven to 400 degrees with a rack in the center position.
Coat four 4-ounce ramekins or muffin cups with pan spray. If using ramekins, set them on a rimmed baking sheet.
Melt the chocolate, butter, and ½ tablespoon of water in a double boiler, or in a microwave, until you can stir the mixture smooth.
Whisk in the salt, yogurt, egg substitute, and vanilla. In a small bowl, stir together the cocoa powder and flour.
Using a standing mixer fitted with a whisk attachment, beat the egg whites on high speed until they are foamy. (Alternatively, use a handheld electric mixer.) With the mixer running, gradually add the sugar, a few teaspoons at a time. After all of the sugar is in, continue to mix until soft, glossy peaks form, curling over when you lift the beater.
Fold the chocolate mixture into the egg whites until mostly combined. Sift half of the cocoa mixture over the top and fold it in with a spatula. Once it is mostly incorporated, sift the remaining cocoa mixture over the top and fold until it is incorporated.
Spoon ¼ cup of the batter into each prepared ramekin. Place 1 teaspoon of the peanut butter in the center of each one, and cover the peanut butter with a heaping tablespoon of batter.
Bake for 15 minutes, or until a toothpick inserted into the cake (not the center) comes out clean. Set the ramekins on a wire rack and let them cool for several hours.
Serve the cakes in the ramekins, or if you used muffin cups, unmold them before serving.
Store any leftover peanut butter cups, tightly wrapped, at room temperature for up to 24 hours.