Preheat the oven to 375º. Generously butter 12 6-ounce ramekins, then coat with sugar.

Whisk together yolks, flour, zest, and half the sugar (¼ cup).

Bring milk to boil in a saucepan. Slowly pour milk into the yolk mixture, whisking constantly to prevent yolks from cooking.

Return mixture to pan and whisk, while cooking, till thick like a pudding, 1-2 minutes. Strain through a sieve, then stir in butter and lemon juice.

Beat egg whites till foamy. Gradually add the remaining ¼ cup sugar and whip till medium-firm peaks form. Stir ⅓ of whites into the yolk mixture. Fold in the remaining whites gently with a spatula.

Fill each soufflé cup to the top, tap to settle, and smooth the top with a spatula. Run your thumb around the inside perimeter of each dish.

Place soufflés on a baking sheet and bake 15-18 minutes till they rise about an inch above the rim but are still jiggly in the center. Lightly dust with powdered sugar and serve immediately with raspberry sauce if desired.

To make the raspberry sauce, cook raspberries and sugar till the fruit is soft and breaks apart. Strain through a sieve. Add a squeeze of lemon juice. Cool before serving.