Place cauliflower, squash, 1 teaspoon sea salt and 1 branch of fresh sage, garlic and water in a large Dutch oven.
Place lid on Dutch oven and turn heat to high. Cook vegetables for 20 minutes, or until veggies are softened and easily pierced with the tip of a sharp knife.
Drain vegetables and remove the sprig of sage. Next, add drained vegetables to the bowl of a food processor, along with the vegan butter, red pepper flakes, black pepper, remaining 1/2 teaspoon sea salt, leaves of remaining sage sprig and nutritional yeast.
Pulse to combine the ingredients, scraping down the bowl as needed, until a smooth puree has been formed.
Serve warm and garnish with additional sage leaves if desired