Upside Down Lemon Pudding Cake

2 large eggs, separated, at room temperature
2 Tbsp. unsalted butter, softened
2/3 cup sugar
2 Tbsp. all-purpose flour
2 Tbsp. lemon zest
1/8 tsp. salt
1/4 cup fresh lemon juice from 2 lemons
1 cup milk

Heat oven to 350 degrees. Grease a 2 quart baking dish or six 6-ounce ramekins. With an electric mixer, beat the egg whites to soft peaks. Transfer to a bowl and set aside. Beat the butter and sugar together until fluffy, about 2 minutes. Add egg yolks and combine, then flour, lemon zest, and salt, and beat until combined. Add the lemon juice and milk and beat until incorporated. Fold in the egg whites. Pour batter into prepared dish or ramekins. Place dishes in a large baking pan and add enough boiling water to the pan so that it reaches halfway up the side of the dish. Bake until the top is golden and the center springs back when gently pressed, 35 to 45 minutes for a large baking dish and 25 to 35 minutes for ramekins. Transfer dishes to a rack to cool completely, at least 1 ½ hours. The pudding cakes can be refrigerated for up to 2 days. Allow to sit at room temperature for 30 minutes before serving. To serve, run a knife around the edges of the dish and invert onto a plate.

This is a good make-ahead dessert for company from America's Test Kitchen.