In a mixing bowl combine the flour, granulated sugar, baking powder, salt, and nutmeg. Stir with a spoon to combine, set aside. In a larger mixing bowl combine the eggs, milk, vegetable oil, cooled & melted butter, and vanilla extract. Stir to combine.
Gradually mix the dry ingredients and 1 ½ cups chocolate chips into the wet ingredients, mixing just until combined. The batter will be very thick! Cover the bowl with a towel and allow the batter to rest for 15 minutes. During this time, preheat the oven to 425ºF / 220ºC. For bakery style muffins, line a 12 count muffin pan with 6 muffins liners, meaning you’ll only fill every other muffin well with batter. Fill the liners with 6-8 heaping tablespoons of batter. Top the muffins with the remaining chocolate chips. Sprinkle them with sanding sugar.
Place one pan in the center of the oven and bake for 7 minutes at 425ºF / 220ºC, then keep the muffins in the oven, turn the temperature down to 350ºF and bake for 12-16 minutes or until a toothpick inserted in the center comes out clean. Allow the muffins to cool in the pan. Repeat with the remaining batter, bumping the temperature back up to 425ºF.