Preheat oven to 350oF. Spray a muffin pan with nonstick cooking spay or line with paper liners.
Melt unsalted butter in the microwave. Set aside.
In the mixing bowl sift together the flour, baking powder, baking soda and salt. Set aside.
In another mixing bowl whisk eggs and sugar until light fluffy. This takes 1-2 minutes on medium speed.
Add sour cream, melted butter and vanilla extract. Whisk again until all combined. Add the dry ingredients and whisk again until evenly combined. Stir in the chocolate chips.
Spoon the batter into the prepared pan, filling the muffin cups about three-quarters full. Sprinkle the tops with more chocolate chips and the coarse sugar.
Bake muffins for 18-20 minutes or until golden brown.
Remove from the oven and let muffins cool in the pan for 5-10 minutes, then transfer muffins to a wire rack to cool completely.