Peel the sweet potatoes and cut them into 1” cubes. Add them to a large pot of water. Place the pot over medium-high heat and bring to a simmer. Cover partially and cook until tender, about 15 minutes.
While the potatoes are simmering, peel and slice the onions. Add them to a large skillet with the Chicken Fat. Place over medium heat and cook until caramelized, stirring occasionally. This should take about 15 minutes. Once caramelized, add the sliced garlic and thyme leaves to the pan. Stir until the garlic is fragrant, about 2 minutes. Set aside about ¼ of the onions for topping the mash, if desired.
Once the sweet potatoes have cooked, drain the water and allow them to steam for about 5 minutes. Add them to the bowl of a large food processor along with the remaining onion and garlic mix (scraping all the chicken fat in, as well), the coconut cream, sea salt, and black pepper. Process until smooth, stopping to scrape down the sides occasionally.
Serve with the reserved caramelized onions over top.