Preheat oven to 350° F with rack in centre of the oven and lightly butter one 1.5 quart baking dish or 4-6 individual, small ramekins. Have ready a high-sided roasting pan and place the prepared dish (or dishein to the roasting pan. Bring 8-10 cups of water to a simmer (will be added to the roasting pan to bake the puddings). Separate your eggs and have ready.
Set aside 2 Tbsp. of the white sugar. Add the rest of the sugar to a large bowl or the bowl of a stand mixer. Add the butter and beat (with stand mixer or electric mixeuntil mixture is grainy but light. Add the egg yolks one at a time, beating well after each addition. Add the lemon zest and mix in. Add the flour and salt and mix. Add the milk and lemon juice and mix until combined. Set aside, or if using your stand mixer, remove to a large bowl and wash your mixer bowl really well (you'll be whipping the egg whites in it next, so be sure it is squeaky clean!).
In another bowl or the bowl of a stand mixer, beat your egg whites until they're frothy and beginning to form soft peaks. Sprinkle in the reserved 2 Tbsp. of white sugar and beat again until stiff peaks form.
Spoon the whipped egg whites on top of the egg yolk mixture. Using a spatula, gently fold the egg whites in to the egg yolk mixture by pulling a bit of the batter up and over the egg whites. Continue working gently until the mixture is uniform in color and texture. Do not over mix, but be sure there aren't any large chunks of egg whites.
Pour or ladle your batter in to the prepared dish or dishes, set in the roasting pan. Carefully pour simmering water in to the roasting pan so it comes about halfway up the sides of the baking dish. Carefully transfer the roasting pan with the water and ramekins in to the preheated 350° oven. Pudding(will bake anywhere from 30 minutes (for small, individual servingto 45 minutes (for one large pudding). Baking times will vary though, so do watch closely. You want the top to be firm and golden, but not browned.
Remove the pudding from the oven and transfer baking dish or dishes to a cooling rack. Allow to cool for 10 minutes before dusting with icing/confectioners sugar. Serve warm and enjoy!
Be sure to read the "Cook's Notes" in the original post, for more tips, options, substitutions and variations for this recipe!