Preheat oven to 400°F. Coat six 8 ounce (or twelve 4 ounce) ramekins with the butter using your fingertips. Dust ramekins with 2 tablespoons of the granulated sugar, rolling it around the sides and emptying the excess out (or right into the next ramekin).

Bring the milk to a boil in a medium-sized heavy saucepan. Remove from heat. Whisk the egg yolks, vanilla, and 1 tablespoon of sugar together in a medium bowl. Whisk in the flour. Whisk 1/4 cup of the hot milk into the egg yolk mixture until blended. Continue mixing the hot milk into the egg yolk mixture 1/4 cup at a time until all the milk is incorporated.

Remove the custard from the heat. Mix the lemon zest, lemon juice, and powdered sugar together in a small bowl. Whisk the lemon mixture into the custard until smooth.

Beat the egg whites on high speed until they reach soft peaks stage. Sprinkle 2 tablespoons of sugar over the egg whites and beat until stiff and shiny.

Fold 1/4 of the egg whites into the custard until the whites disappear. Fold in the remaining egg whites until just blended – don’t over blend or you’ll deflate the egg whites and the batter will turn soupy.

Spoon the batter into the ramekins. Fill the ramekins to just the top, level the tops with a knife (like you would a cup of flour...one quick scrape). Use your finger to go around the perimeter of each ramekin to both clean the edges and to "edge" the batter from the rim.

Reduce the oven to 375°F and immediately place your ramekins into the oven on a baking sheet. Bake until puffed and the tops turn golden brown, about 12-14 minutes for the 8 oz ramekins and 11-12 for the smaller ones. They should still be wobbly when you take them out of the oven.

Give them a liberal dusting of powdered sugar and you are good to go! You can also choose to serve them with fresh whipped cream and berries on the side.

Serve immediately.