Preheat your oven to 425°F. Wash the sweet potato thoroughly and poke it several times with a fork to allow steam to escape during roasting. This prevents the potato from bursting and ensures even cooking. Place it directly on the oven rack with a baking sheet below to catch any drips, then roast for about 60 minutes until completely soft and a fork easily pierces the flesh. The potato should yield slightly when squeezed (use an oven mitt!). Once done, remove from the oven and let cool for 10-15 minutes until comfortable to handle.

While the sweet potato cools, melt the butter in a small saucepan over low heat, then set aside. Once the roasted sweet potato is cool enough to handle, scoop the flesh into a large bowl and mash it with a fork or potato masher until smooth—don't over-mix or it can become gluey. Add the melted butter, sweetened condensed milk, light brown sugar, vanilla extract, cinnamon, and nutmeg to the mashed sweet potato. I like to add the spices early so they distribute evenly throughout the filling and bloom together, creating deeper, more complex flavor notes.

Reduce your oven temperature to 350°F. Gently whisk the eggs in a small bowl until just combined and smooth. Add them to the sweet potato mixture from Step 2 and stir until everything is fully incorporated and the filling is uniform and creamy. I find whisking the eggs separately first prevents streaking and ensures they cook evenly throughout the pie. Pour the filling into your prepared graham cracker crust, smoothing the top with a spatula if needed.

Place the pie on the center rack of your preheated 350°F oven and bake for 30-40 minutes, until the edges are set and firm but the center still has a very slight jiggle when you gently shake the pan—this indicates a creamy, custard-like texture inside. The top should be lightly golden. Remove from the oven and let cool completely at room temperature for at least 1 hour before slicing. For the best texture and flavor development, I recommend chilling the pie in the refrigerator for at least 4 hours or overnight, which also makes it much easier to slice cleanly.