CAKE PREPARATION: For The cake, coat a 3-quart bundt or tube pan with 1 tablespoon of the butter and dust pan with 1 tablespoon of the flour. Separate the eggs and set aside.
Grate 2 teaspoons lemon zest and squeeze 1/3 cup lemon juice. Beat remaining butter and the sugar in a bowl until the mixture is light and fluffy. Beat in egg yolks, one at a time. Beat in lemon zest, lemon juice and yogurt.
Sift remaining flour with baking powder, baking soda and salt. Turn mixer to low and beat in dry ingredients until just incorporated. Turn mixer to medium, beat for 2 minutes.
With clean beaters, whip whites to firm peaks and fold into batter. Pour batter into prepared pan.
Adjust oven rack to middle position and preheat oven to 350. Bake until a cake tester inserted in the center of the cake comes out clean, about 50 minutes. Cool cake in the pan for 10 minutes, then invert onto a wire rack to cool completely. (Can wrap and store at room temperature overnight, or freeze for up to 1 month.)
GLAZE: Sift confectioners' sugar into a medium bowl or large measuring cup. Squeeze in 1 tablespoon lemon juice and stir in yogurt until glaze is smooth.
With cake on a wire rack set over a pan to catch drippings, pour glaze over the cake, allowing it to drip down the sides. Let cake stand at room temperature until glaze sets, about 10 minutes. (Can cover and store at room temperature for up to 2 days.)