To make the muffins:
Cream the butter and the sugar in a large mixing bowl on medium speed until light and fluffy, about 2 to 3 minutes.
Lightly whisk the egg yolks, and then add them to the butter and sugar mixture. Beat together on medium speed about 1 minute until well combined.
In a separate bowl whisk together the flour, baking powder and kosher salt.
Add the flour mixture alternately with the lemon juice, blending in on low speed, beginning and ending with the flour. Beat just until the ingredients are blended together.
Stir in the lemon zest, vanilla and lemon extract using low speed.
Beat the egg whites in a separate bowl on medium speed until stiff peaks form, about 1 to 2 minutes.
Using a spatula, gently fold the egg whites into the batter.
Line 20 muffin cups with parchment liners. Using a large ice cream scoop fill the cups about ¾ full.
Bake the muffins in a 375-degree oven for 22 to 24 minutes or until they test done with a toothpick in the center. The muffins will still be light in color on top.
Let the muffins cool in the pan for about 5 minutes then finish cooling on a wire rack.
To make the glaze:
Whisk together the powdered sugar with 3 tablespoons of the remaining lemon juice. Add all the lemon juice if you want a thinner glaze.
Drizzle the glaze over the tops of the cooled muffins.