1. Preheat oven to 350 and grease 12 cup muffin tin.
2. Melt butter
3. Add brown sugar to a large bowl and pour butter over it.
4. Stir to combine and let stand for 5 minutes.
5. Add egg and egg yolk. Stir to combine.
6. Add flour, baking soda, and salt. Stir until just combined.
7. Stir in chocolate chips.
8. Using tablespoon, stop 2 loaded tablespoons in each muffin cup.
9. Bake 7-10 minutes or until edges of the cookies are golden brown.
10. Let cool in muffin tin for 5 minutes. Remove to wire rack to finish cooling