Heat oil in a Dutch oven over medium heat. Cook onion and carrot with a pinch of salt for 7 to 9 minutes, until softened but not dark.
Add apple, garlic, sage and nutmeg. Cook 2 minutes, stirring, until fragrant.
Add squash, 3 1/2 cups broth, salt and pepper. Bring to a boil, reduce to a steady simmer, cover partly and cook 18 to 24 minutes until the squash crushes easily.
Remove from heat and cool 5 minutes. Blend with an immersion blender until completely smooth, keeping the head submerged to limit splashing.
Return to low heat. Add optional cream and enough reserved broth to reach the preferred thickness.
Stir in vinegar, taste for salt and pepper, and serve with sage, pepitas or black pepper.