Step 1
Line muffin tins with paper liners or grease with butter. Adjust oven rack to middle position and preheat oven to 350°F.
Step 2
In a medium bowl, whisk together oats, flour, sugar, baking powder, and salt. Set aside.
Step 3
In a small bowl, whisk together milk, sour cream, and egg. Add to dry ingredients and stir until just combined. Stir in chocolate chips. Let batter stand 5 minutes for oats to absorb some liquid. Pour batter into muffin cups, filling 3/4 way. Bake until a cake tester inserted in the middle of a muffin comes out clean, about 12 minutes. Let cool completely before storing in an airtight container for up to 2 days.