In a large bowl, cream butter and sugars together. Add egg and buttermilk. Mix together until well combined. Add flour, baking powder, baking soda, and salt. Mix until just combined. Fold in chocolate chips, leaving some to sprinkle on top.
Cover the bowl with a kitchen towel and let the mixture rest for at least 1 hour. If you want to get those pretty domes, do not skip this step.
Preheat the oven to 425ºF. Spray a 12 cup muffin tin with nonstick cooking spray. Divide batter evenly into the prepared muffin tin, filling each muffin cup 3/4 full.
Place the muffin tin in the oven and immediately turn down the heat to 350ºF. The initial high heat activates the leaveners (baking soda/baking powder) to create those pretty domed muffins.
Bake for 20-22 minutes or until a toothpick inserted into the center of a muffin comes out clean. Let cool and serve. Enjoy!