Heat oven to 350°F. Lightly grease a standard sized bread pan with butter.
Whisk flour, baking powder, kosher salt, and baking soda in a medium bowl. Whisk sour cream, milk and lemon juice in small bowl to blend. Using electric hand mixer, beat sugar, butter, and lemon zest in large bowl to blend. Add eggs,1 at a time, beating well after each addition until mixture is light and fluffy, scraping down sides of bowl as needed.
Beat in dry ingredients in 3 additions, alternating sour cream/milk mixture in 2 additions. Mix just until blended. Stir in poppy seeds. Spoon batter into prepared pan.
Bake until toothpick inserted into center comes out clean, about 40-50 minutes.
Remove from oven and cool in pan 10 minutes, then remove from pan and transfer to a wire rack to cool completely.
FOR THE GLAZE
Mix together melted butter, lemon juice and enough powdered sugar to make a glaze of the consistency you'd like to use. Use an offset spatula to spread or drizzle glaze as desired. To thicken glaze, add more powdered sugar. To thin glaze, add water or milk, 1 teaspoon at a time.