Soak the cashews in water for at least 30 minutes or up to 2 hours. Discard the water when done.
Using a steamer basket or the microwave, steam the cauliflower until just tender.
While the cauliflower is steaming, heat the coconut oil or ghee in a skillet over medium-high heat. Add onions and sauté for about 3-4 minutes. Next add the garlic and cumin and sauté for another 2-3 minutes.
Add the onion sauté, cauliflower, milk, lemon juice, nutritional yeast, salt, and pepper into a food processor or high speed blender and blend until very smooth and creamy. Adjust liquid by adding more milk (or leftover cauliflower steaming water) if you prefer a thinner sauce.
Season as needed with salt and pepper, then serve warm with your choice of food.