Line pan with cupcake liners or grease the pan (I used Baker's Joy).
Melt together Butter and Chocolate Chips in saucepan. Stir until smooth.Let cool! If you DO NOT let it cool, the mixture will COOK your egg whites and leave a stringy white swirl in your brownies. It should NOT be hot.
Combine Eggs, Sugar, and Vanilla. Mix well.
Mix in the COOLED Chocolate Mixture.
Mix in Flour BUT do not completely mix in the Flour before you add in the Chocolate Chips.
Combine ingredients until smooth. Do Not overmix. Once it's smooth—you're done!
Fill your cupcake cups half full.
Bake 20-30 minutes or until a tester comes out with a few dry crumbs.
Remove from pan to cool so your cupcakes don't keep baking and over-bake.