Preheat a conventional oven to 375 degrees or a convection oven to 350 degrees. Butter six 10-ounce souffle dishes, then dust with granulated sugar. Whisk together yolks, flour, zest, and 2 tablespoons granulated sugar.
Bring milk to a boil in a small saucepan. Slowly pour milk into yolk mixture, whisking constantly to prevent yolks from cooking. Return mixture to pan and whisk until thick like a pudding, 3 to 4 minutes. Whisk in butter and lemon juice.
Whisk whites until foamy. Gradually add remaining 1/4 cup plus 2 tablespoons granulated sugar and beat until stiff peaks form. Stir one-third of the whites into yolk mixture. Gently fold in remaining whites using a rubber spatula.
Fill each souffle dish to the top; smooth. Run your thumb around edges to remove batter from rims.
Bake on a rimmed baking sheet until souffles rise and are golden, about 16 minutes. Dust with confectioners' sugar and serve immediately with raspberry sauce before souffles lose their height.