Bring a large pot to medium-high heat. Add the vegan butter and let it melt. Sauté the onions for 3 minutes. Add the carrots and garlic. Stir as they cook for 2 minutes.
Mix the cornstarch into the plant-based milk until it’s lump-free. Stir in the vegetable broth, plant milk/cornstarch mix, and all the seasoning to the pot.