Preheat the oven to 375 degrees. Butter and flour a 9-inch round pan and set aside.
In a mixing bowl, using an electric mixer set on high speed, blend the butter and the 1 cup granulated sugar together until light and fluffy, about 5 minutes. Add the egg yolks, one at a time, mixing well after each addition. Add the lemon juice, zest, and baking powder and mix well.
Slowly stir in the flour and milk. Mix on low speed until combined.
In another bowl, whip the egg whites with the electric mixer set on high. When the egg whites begin to get frothy, sprinkle with the 2 tablespoons granulated sugar. Continue beating until the egg whites form soft peaks.
Gently stir about one-quarter of the whites into the cake batter to lighten it. Fold in the remaining whites until just combined, being careful not to overmix. Pour the batter into the prepared pan and bake for about 30 minutes, or until golden and a toothpick inserted in the center comes out clean.
Allow the cake to cool on a rack in the pan for 10 minutes, then invert onto a serving platter and allow to cool completely.
To make the glaze, whisk together the confectioners' sugar and lemon juice until smooth. Pour half of the glaze over the top of the cooled cake, allowing it to drip down the sides. Allow the cake to stand for 10 minutes, then top with the remaining glaze.
Garnish with the lemon zest and candied violets, if using, and serve.