Heat oven to 350°F (175°C). Line a 12-cup muffin tin with liners or grease well.
Roast a whole sweet potato at 400°F until soft (45–60 minutes), or peel/chop and steam until fork-tender (10–12 minutes). Cool, then mash.
Add in this order: yogurt, eggs, maple syrup, oil, vanilla, mashed sweet potato. Then add oats, baking powder, baking soda, cinnamon, nutmeg, and salt.
Blend on medium until smooth and the oats are fully broken down, 30–60 seconds. Scrape sides and blend again briefly. Batter should be thick but pourable.
If using chocolate chips or nuts, pulse once or fold in by hand to avoid over-blending.
Divide batter evenly among 12 cups (about 3/4 full). For bakery tops, sprinkle a few oats or turbinado sugar on each.
17–21 minutes, until tops spring back and a toothpick comes out clean or with a few moist crumbs.
Let muffins rest in the pan 5 minutes, then transfer to a rack. This sets the crumb and prevents soggy bottoms—nobody asked for those.
Enjoy warm or at room temp. Add a smear of nut butter if you're feeling extra.