Preheat oven to 425 and prepare a rimmed cookie sheet with parchment.
In a large bowl, toss cauliflower, sweet potato and garlic with oil, salt and pepper and pour onto cookie sheet.
Tuck garlic between other veggies so it's less likely to burn.
Roast for 20 minutes, check that garlic isn't burning and roast for 10 minutes more. Garlic should be soft, the cauliflower starting to brown and everything fork tender. Carefully set garlic aside.
Add roasted vegetables to the food processor, squeeze garlic out of its skin and add to food processor along with butter, sage and maple syrup. Puree until well blended, then, start drizzling in cashew milk to achieve desired consistency.
I added just over 1/4 cup to create a smooth texture. Taste, and adjust salt or maple syrup if necessary.
Tip: You can absolutely mash this recipe by hand, which will result in a more rustic mash but it is absolutely delicious.