Preheat the oven to 375°F. Coat the muffin tin with cooking spray or butter (optional: use muffin paper liner).
In a large bowl: beat sugar, eggs and mix. Add oil, vanilla extract, sour cream and mix until well combined.
Add in the flour, baking powder, baking soda, salt and mix. Highly recommend that you sift the dry ingredients before mixing with the wet ingredients to form a smoother batter. This will make the muffins very soft & fluffy (don't skip this tip).
Add 1 ½ cups of chocolate chips and use a spatula to fold the batter.
Divide batter into even portions into the muffin tin (should be exactly 12). Sprinkle the other ½ cup of chocolate chips on top of the batter.
Bake for 18 minutes. Do not over bake the muffins or it will be dry.
Let the muffins cool in the tin for about 10 minutes and then transfer them to a baking rack to finish cooling completely.