Preheat oven to 350°F. Grease 20 muffin pan cups w/ butter or cooking spray. Or be awesome and get these. Sift dry ingredients (using only 1/4 c. sugar) with a big strainer into a large bowl; set aside. In another bowl, mix everything else except egg whites.
Beat egg whites in a deep bowl at medium speed with an electric mixer until foamy. Turn mixer to high and gradually add remaining 1/2 cup sugar, until glossy, stiff peaks form. Stir yogurt mixture into flour mixture just until dry ingredients are moistened. Gently fold in 1/3 of egg whites until blended; fold in remaining egg whites. Spoon batter into muffin cups, filling 2/3 full.
Bake 20 minutes or until toothpick inserted into centers comes out clean. Transfer cupcakes from pans to wire racks; cool completely. Meanwhile, make the Sugar Glaze; drizzle over cupcakes. Eat at least two or three while the glaze is still runny and let the rest set.
Mix yogurt, vanilla, lemon zest and juice in a medium bowl. Add confectioner's sugar and blend with an electric mixer, adding more sugar until it reaches drizzle consistency. I got a little crazy here and started shaking in the sugar straight out of the package while the mixer was running until it was drizzle consistency. And instead of "drizzling", I kind of dumped it on by the spoonful so it was all running down the sides. Total awesomeness.
*Yogurty Note: Fage "Total" Greek yogurt is so f-ing excellent. You'll should add it to everything. You should also eat some of it straight out of the container with a spoon, maybe with some honey. But t's so beautiful, it doesn't really need anything. Can be found @ Trader Joe's, Whole Foods, etc.
**Waste Not, Want Not: Use the the lemon juice from the remaining lemon for something else... like a basic lemon vinaigrette: Pour lemon juice, a little salt and a grind of pepper into a small bowl. Whisk in 1/3 cup olive oil in a slow stream. Your salads and veggies will be very happy.