Preheat your oven to 180°C (350°F). Line a muffin tin with paper liners for easy removal.
In a large bowl, whisk together pumpkin puree, melted butter, and brown sugar until the mixture is smooth and fragrant with warm spices.
In a separate bowl, sift together the flour, baking powder, baking soda, cinnamon, and nutmeg, creating an even dry mixture.
Gradually fold the dry ingredients into the wet mixture using a spoon or whisk until just combined. A few lumps are okay; avoid overmixing to keep the muffins tender.
Divide the batter evenly among the muffin cups, filling each about two-thirds full—this helps prevent overflow and ensures a rustic, cracked top.
Bake in the preheated oven for 20–25 minutes, until the tops are golden and cracked, and a toothpick inserted in the center comes out clean.
Remove the muffins from the oven and let them cool in the tin for about 5 minutes, which helps set their shape.
Transfer the muffins to a wire rack to cool slightly, revealing their rustic, cracked tops and moist crumb. Serve warm with a smear of butter for the ultimate cozy treat.