Preheat the oven to 400 degrees F. Lightly grease 2 mini muffin tins (each with 12 (1 3/4-inch) wells) with 1 tablespoon softened butter and set aside.
In a large bowl, sift together cake flour, flour, baking powder, baking soda, salt, and poppy seeds.
In a medium bowl, combine the egg and sugar and beat with an electric mixer on high speed until light and fluffy, about 2 minutes. Reduce the mixer speed to medium and beat in the yogurt, remaining 4 tablespoons of butter, lemon juice, zest and vanilla until well incorporated, about 30 seconds. Fold the wet ingredients into the dry just until moistened and being careful not to over-mix. Divide the batter among the prepared muffin tins, filling each halfway.
Bake until the muffins are set and golden brown and a tester comes out clean, 14 to 16 minutes.† Remove from the oven and use a toothpick to poke several holes in the top of each muffin. Brush each muffin generously with the lemon glaze.† Allow the muffins to cool for 10 minutes in the tin and then transfer them to a wire rack to cool completely.
Yield: 2 dozen