Grate the zest from the lemons into a medium mixing bowl to get about 1 heaping tablespoon. Juice the lemons into a small bowl to get about 4 tablespoons and set aside.
Cream the butter with the lemon sugar with a sturdy whisk or using a hand blender. Add the egg yolks and beat again until well mixed. Add the flour and salt and mix on low speed until blended. It will be very thick and stuck in the whisk or beaters, but will release once you add the liquids.
Add the reserved lemon juice followed by the milk and mix until it is smooth and thick as pancake batter.
In a separate bowl, beat the egg whites until they form soft peaks. Gently fold the whites into the batter to make an airy batter. Distribute the batter into the ramekins. Push 5 or 6 raspberries into the batter in each of the ramekins.
Set the baking dish on the oven rack and pour the boiling water into it to reach 1 inch up the sides of the ramekins.
Bake for 40 to 45 minutes until the puddings are set. (You can check the center with a knife.) They will be puffed up and deeply golden brown on top.
Cool on a rack and serve warm or chilled with a dusting of confectioner's sugar, if desired.