Position a rack in the top third of the oven; preheat to 350 degrees. Butter eight 6-oz. ramekins or small mason jars. In a large bowl, whisk 1/2 cup plus 2 tbsp. sugar, the flour and a pinch salt. In a medium bowl, whisk the milk, egg yolks and lemon zest and juice. Add the milk mixture to the flour mixture and whisk until smooth.
Using an electric mixer, beat the egg whites until foamy. With the mixer running, gradually add the remaining 1/4 cup sugar; beat until soft peaks form. Add one-third of the egg-white mixture to the lemon mixture; whisk until just blended. Fold in the remaining egg-white mixture. Divide among the ramekins.
Place the ramekins in a large roasting pan. Pour in hot water to come halfway up the sides of the ramekins. Bake until the tops start to brown and the cakes begin to pull away from the sides, about 25 minutes. Using tongs, carefully remove the ramekins from the pan; let cool. Cover and refrigerate until cold, about 4 hours or overnight. Dust with confectioners' sugar, if using.