In a large bowl, combine the oats, yogurt, and milk and let them sit for at least an hour (you could also combine them in a jar the night before you plan on baking and keep them in the fridge).

When you're ready to bake, preheat the oven to 425F.

Add the egg and melted butter to the oat mixture and stir to combine.

In another bowl, whisk together the flour, sugar, salt, baking powder, baking soda, cinnamon, and nutmeg. Add to the oat mixture and stir until just incorporated.

Divide batter between 12 lined muffin cups.

Bake for 18-20 minutes, until a cake tester comes out clean.