Heat your oven to 350 degrees. Pierce the sweet potatoes several times with a fork and place on the middle rack. Bake until potatoes are soft.
Scoop the flesh of the sweet potatoes out into a large bowl while still warm. With a potato masher, mix in 3 tablespoons of butter, spices, salt, sugar, ginger and the egg yolks. Beat until the mixture is smooth and creamy. If you want to get fancy, you can spoon the potato mixture into a piping bag with a star tip and pipe into a buttered baking dish, or you can spread the sweet potatoes into a buttered, 9-inch baking dish and then use a fork to create peaks on the surface. It’s up to you.
Melt the remaining tablespoon of butter and brush over the top of the potato peaks. Bake the dish at 425 degrees until nicely browned on top, about 20 minutes. Sprinkle with toasted pecans and serve or store for up to 3 days in the fridge. Reheat before serving.
Tip: Toast pecans by putting them into a dry skillet over medium heat and stirring until they begin to smell nutty.