Position oven rack in center of oven and preheat oven to 350°F. Grease 1½ quart casserole or 8”x8” baking dish. In small bowl, whisk the flour, baking powder, and salt together. Set aside.

Heat water for the pudding’s bain marie (hot water bath).

In bowl of stand mixer fitted with paddle attachment, cream the butter. Gradually beat in the sugar. Beat in the egg yolks, one at a time, mixing well after each addition. Beat in the lemon juice and lemon zest.

Add the flour alternately with the milk, starting and ending with flour (3 additions of flour and two of the milk), stopping to scrape sides of bowl as necessary.

In separate clean bowl, whip the egg whites at high speed with the whisk attachment of the stand mixer or, alternatively, with a small hand mixer until soft peaks form.

Using a rubber or silicone spatula, fold about half of the egg whites into the lemon mixture then fold in remaining egg whites. Do not overmix or stir mixture in; use the folding technique. Transfer mixture to prepared baking dish.

Place the dish containing the pudding in a high-sided baking pan or roaster that allows at least an inch of space all around the pudding dish. Place the baking pan or roaster containing the pudding dish on the oven rack and carefully pour hot water into the pan, filling it one-half way up the side of the pudding dish.

Bake for about 40-45 minutes, or until top of pudding is golden tanned and top springs back from a light touch. Carefully remove the pudding dish from the water bath and transfer to wire rack to cool to lukewarm or room temperature before serving. Pudding may also be served chilled. Dust pudding with icing sugar and/or additional lemon zest, if desired.