In a small saucepan over low heat, melt butter. Let it come to a low boil and add sage leaves. Continue to let butter cook at a low boil. Scrape the bottom from time to time to make sure that nothing is sticking to the bottom and burning.
When you see that little light brown bits are starting to bubble to the top and it smells nutty like toffee, it is done. Remove the sage leaves and let them drain on paper towels. Turn the heat off and set the butter aside.
Once the foam/bubbles settle down, the browned butter looks... well, browned!
For the Sweet Potatoes:
While the butter is cooking, peel and cut sweet potatoes into large chunks. Boil in a large pot of water until fork tender.
Drain the water from the sweet potatoes and add browned butter and remaining ingredients. Using a hand mixer, whip until all of the ingredients are combined.
Pour sweet potatoes into a serving bowl and garnish with the cooked sage leaves (or fresh if you prefer).