Scrape down bowl before then adding oil and eggs. Mix together until combined. Follow up by adding sour cream (or Greek yogurt) and milk and mixing well.
Pour wet ingredients into bowl of dry ingredients. With a spatula, fold together all ingredients until just combined. Then fold in the chocolate chips and blueberries.
Avoid over-mixing, as it can result in a dry muffin.
Distribute batter evenly into the pan, filling each muffin cup to the top. Sprinkle about half a teaspoon of turbinado sugar onto each of them for added crunch and texture. Bake at 425°F for 5 minutes, then, keeping the muffins in the oven, lower the temperature to 375°F.