10 Tbsp unsalted butter (1 1/4 stick), softened
2 Whisk together the flour, baking powder, baking soda, poppy seeds, and salt and set aside.
3 In a large mixing bowl, cream butter and sugar together, beating until fluffy (about 2 minutes with an electric mixer). Add eggs one at a time, beating until incorporated after each one. Add the buttermilk and sourcream. Beat in the lemon zest.
4 Now add the dry ingredients. Mix until all is moist. Do not over beat.
5 I used a standard 12-muffin muffin pan and had enough batter leftover to fill 3/4 of my mini muffin tin. Spray each muffin tin with cooking spray or brush with butter. Distribute the muffin dough equally among the cups. Bake until muffins are golden brown, about 2o minutes(less for the mini muffins). Test with a long toothpick to make sure the center of the muffins are done. Set muffin pan on wire rack to cool. After 5 minutes, remove muffins from pan.
6 While the muffins are cooling, in a bowl, whisk together the powdered sugar and lemon juice for the glaze. Add more lemon juice if necessary. While the muffins are still a bit warm, use a pastry brush to brush the glaze over each muffin. The muffins will absorb some of the glaze, so you add more glaze to each muffin if you like.
Makes 12 muffins. Best eaten fresh and warm.