Lemon Pudding Cake

This pudding cake can be made in any of the following: six 3⁄4-cup custard cups, four 1-1⁄3-cup ramekins or miniature soufflé cups, one 9-inch round cake pan, or one 8-inch square cake pan. All pudding cakes, regardless of pan size, require the same baking time.

1. Adjust oven rack to middle position and heat oven to 325 degrees. Grease pan or baking molds of choice. Lay folded kitchen towel in bottom of roasting pan and set molds or pan inside. Bring kettle of water to boil.
2. Meanwhile, using back of wooden spoon, mash butter, sugar, and salt together in medium bowl until crumbly. Beat in egg yolks, then stir in flour, mixing until smooth. Slowly beat in lemon zest and juice, then stir in milk. Using stand mixer fitted with whisk, whip egg whites and cream of tartar on medium-low speed until foamy, about 1 minute. Increase speed to medium-high and whip until stiff peaks form, 3 to 4 minutes. Gently whisk whites into batter by hand just until no large lumps remain.
3. Immediately ladle (do not pour) batter into pan or baking molds of choice. Set roasting pan on oven rack. Quickly pour enough boiling water into roasting pan to come halfway up sides of pan or molds. Bake cake until center is set and springs back when gently touched, about 25 minutes. Remove roasting pan from oven and let pan or molds continue to sit in water bath for 10 minutes. Serve warm, at room temperature, or chilled.

ORANGE PUDDING CAKE
Reduce lemon juice to 2 tablespoons and add 1⁄4 cup orange juice with lemon juice in step 2. Substitute 1-1⁄2 teaspoons orange zest for lemon zest.

COFFEE PUDDING CAKE
This cake tastes best when made with very strong coffee. The easiest way to make it strong is to cover 1⁄3 cup finely ground coffee with 2⁄3 cup boiling water and let it stand for 5 minutes, then drip through a coffee filter.
Substitute 1⁄3 cup room-temperature brewed strong coffee and 2 tablespoons coffee-flavored liqueur for lemon juice and zest. Decrease sugar to 1⁄2 cup and flour to 2 tablespoons.

CHOCOLATE PUDDING CAKE
Slowly stir 1⁄2 cup boiling water into 1⁄3 cup cocoa. Cool paste slightly, then stir in 1 tablespoon dark rum. Substitute cocoa paste for lemon zest and juice. Decrease flour to 2 tablespoons.