Preheat your oven to 425°F (220°C). Wash and dry the sweet potatoes thoroughly, then pierce each one 8-10 times with a fork to prevent bursting during roasting. Pro tip: Don't skip the piercing step – it prevents messy explosions in your oven!

Place the pierced sweet potatoes directly on the oven rack with a baking sheet on the rack below to catch any drips. Roast for 45-60 minutes, until they're very tender when pierced with a fork. Pro tip: They're done when they feel soft and may even start to caramelize and leak slightly.

Remove the roasted sweet potatoes from the oven and let them cool for 10-15 minutes until safe to handle. The skins should slip off easily when gently peeled with your fingers or a paring knife. Pro tip: If the skins are stubborn, the potatoes may need a few more minutes of roasting time.

Place the peeled sweet potato flesh in a large mixing bowl. Using a potato masher, mash until mostly smooth with just a few small lumps remaining. Pro tip: Don't overmash, as this can make the sweet potatoes gluey. A few small lumps add nice texture.

Add the room temperature butter and mash until well incorporated and the mixture becomes creamy. Pro tip: Room temperature butter mixes more easily and creates a smoother texture than cold butter.

Gradually add the heavy cream, starting with 2 tablespoons and adding more as needed to reach your desired consistency. The mixture should be creamy but not soupy. Pro tip: Add cream gradually – you can always add more, but you can't take it out!

Stir in the brown sugar, salt, cinnamon, and nutmeg. Taste and adjust seasonings as needed. Serve immediately while warm, or keep warm in a slow cooker on low heat. Pro tip: These taste even better after sitting for a few minutes, allowing the flavors to meld together.