Preheat the oven to 375 degrees. Line a standard muffin pan with 9 unbleached parchment liners.Combine baking powder, salt, oats and nuts in a large bowl.In a separate medium bowl whisk together maple syrup, milk, egg, melted butter and vanilla (or combine them in a blender.)Pour the wet mixture into the dry mixture and stir to combine. You can certainly add chocolate chips or fruit to this mixture if you want all the cups to be the same.Ladle the oat mixture into the prepared muffin tin, filling each cup about ¾ full. Sprinkle any additional nuts, berries or chocolate chips over the tops of each.Bake for 20-25 minutes or until set and wet ingredients are fully absorbed. Eat warm or at room temperature. Leftovers can be stored in the refrigerator and eaten straight away or warmed in a toaster oven at 350 until heated through.