Instructions:
- Preheat oven to 400°F (200°C). Pierce sweet potatoes several times with a fork. Roast directly on the oven rack or a baking sheet until completely tender (approx. 45–60 mins). Alternatively, peel, chop, and boil until fork-tender (20 mins).
- While potatoes cook, melt the butter in a small saucepan over medium heat. Continue cooking, swirling occasionally, until the milk solids turn deep amber brown and the butter smells nutty. Immediately pour into a small heatproof bowl to stop cooking and let cool slightly.
- Scoop the cooked sweet potato flesh into a large bowl. Add the warm brown butter (including the browned bits!), brown sugar, egg, milk, vanilla, cinnamon, nutmeg, zest, salt, and pepper.
- Mash or whip the mixture until smooth and creamy. Taste and adjust seasoning as needed.
- Spread the sweet potato mixture evenly into a prepared 9x13 inch baking dish and smooth the top.
- Arrange the mini marshmallows evenly over the sweet potato surface, ensuring full coverage. Bake at 350°F (175°C) for 15–20 minutes, or until the filling is heated through and the marshmallows begin to soften.
- Switch the oven to Broil (High). Watch constantly, and broil for 1–3 minutes until the marshmallows are puffed, bubbly, and deeply golden brown in spots. Remove immediately from the oven.
- Let stand for 5–10 minutes before serving.