Preheat oven to 425°F. Grease 10 standard size muffin tins and line with cupcake liners. Set aside.
In a large mixing bowl combine the melted butter and granulated sugar, beating until combined. Add the eggs in one at a time. Add the greek yogurt, buttermilk and vanilla extract.
Add the flour, baking powder, and salt. Mix until it begins to come together (not fully incorporated). Fold the chocolate chips into the batter, mixing only until combined. Batter will be thick.
Scoop batter into prepared muffin tins, filling about 3/4 of the way. You can use a lage cookie scoop or a 1/4 cup measure to keep things consistent. Sprinkle tops with granulated sugar, if desired.
Bake for 5 minutes at 425°F, then turn oven down to 375°F and bake for an additional 15 minutes, until muffins are golden brown and spring back to the touch. Remove from oven and allow to cool for at least 15 minutes before eating!