Chop peeled potatoes into 1 inch cubes. Add to a large pot and cover with water. Add 1 tsp. salt to the water. Put pot on high and bring to a boil. Once boiling, reduce to medium and let cook until fork tender. When finished, drain and return to the pot.
While potatoes cook, remove crust from bread and chop into small cubes. Melt 4 tbsp. of the butter, and add the bread cubes to the melted butter. Add half the sage leaves and stir well to mix.
Add the milk and remaining butter to the pot. Using a hand held mixer, blend the mixture well until light and whipped. Taste for seasoning and add salt and pepper as desired.
Transfer sweet potato mixture to a casserole dish and top with breadcubes. Put in the preheated oven and bake 20-25 minutes, or until bread cubes are golden brown. If cubes get too brown, tent with foil.
Remove from oven and garnish with remaining sage. Serve immediately.