Ingredient:

• 2 sweet potatoes, quartered lengthwise
• 1 butternut squash, quartered and seeded
• 2 tablespoons olive oil, or as needed
• 3 tablespoons butter
• ½ yellow onion, chopped
• 2 cups milk
• 2 tablespoons all-purpose flour
• 1 ½ teaspoons minced fresh sage, or more to taste
• 1 pinch garlic salt, or to taste
• ground black pepper to taste
• ¼ cup grated Asiago cheese