1. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Sift together flour, cocoa, espresso powder, baking powder, and salt.
2. Place butter in a large bowl; beat with a mixer at medium speed 1 minute. Add granulated and brown sugars, beating until well blended (about 5 minutes). Add egg substitute and vanilla, beating until well blended. Fold flour mixture into sugar mixture; fold in chocolate. Divide batter evenly among 10 (4-ounce) ramekins; arrange ramekins on a jelly-roll pan. Cover and refrigerate 4 hours or up to 2 days.
3. Preheat oven to 350°.
4. Let ramekins stand at room temperature 10 minutes. Uncover and bake at 350° for 21 minutes or until cakes are puffy and slightly crusty on top. Sprinkle evenly with powdered sugar; serve immediately.