Slice the peeled and clean sweet potatoes into 1/2 inch slices.
Place the sliced sweet potatoes into a large pot and cover them with water. On medium to high heat, allow them to boil for 15 - 20 minutes or until fork tender.
Drain the water off the potatoes and set them aside.
Preheat the oven to 350°.
In a medium saucepan on medium heat, add butter and allow it to melt. Once melted add in the sugar, brown sugar, cinnamon and nutmeg. Mix until its fully combined.
Once everything is fully combined, cut off the heat and stir in the vanilla.
Butter or spray the bottom of your baking dish then add in your parboiled sweet potatoes. Pour the mixture over the potatoes making sure they are fully covered.
Bake for 30 minutes uncovered. Halfway through spoon the sauce over the yams. The sauce will bubble.