Pudding cakes are little culinary marvels. Take what is basically a thin cake batter, fold in whipped egg whites, put the batter into a baking dish (or several ramekins as I do here), and voilà! As it bakes, the batter separates and forms a sponge cake on the top with a thick, kind of custardy pudding on the bottom. Lemon pudding cakes are common in the South, but I've swapped lemon for Key lime juice.
To coat the insides of the ramekins with sugar, grease them with nonstick cooking spray or butter, put 1 tablespoon sugar in one, and then tilt and turn it around, tapping to coat all the inside surfaces. Tap the excess sugar into the next ramekin and repeat the process until all are dusted, adding more sugar as needed.