Combine 1/2 cup sugar and water in a small, heavy saucepan, and cook over medium-high heat until sugar dissolves, stirring frequently. Continue cooking 10 minutes or until golden, stirring constantly. Immediately pour into 6 (6-ounce) custard cups coated with cooking spray, tipping quickly until caramelized sugar coats bottom of cups.
Combine milk and espresso in a medium saucepan over medium heat; cook 5 minutes or until espresso dissolves (do not boil).
Remove from heat; stir in 1/4 cup sugar and Kahlua.
Combine eggs and egg whites in a large bowl; stir well with a whisk. Gradually add hot milk mixture to egg mixture, stirring constantly. Divide mixture evenly among prepared custard cups.
Place cups in a 13 x 9-inch baking pan; add hot water to pan to a depth of 1 inch.
Bake at 350 for 50 minutes or until a knife inserted in center comes out clean.
Remove cups from pan; cool completely on a wire rack. Cover and chill at least 8 hours.
Loosen edges of custards with a knife or rubber spatula.
Place a dessert plate, upside down, on top of each cup, and invert custards onto plates.
Drizzle any remaining caramelized syrup over custards.
