Preheat the oven to 400 degrees Fahrenheit. Brush the cut sides of both squash halves with 1 tablespoon of the olive oil and season with a pinch of salt. Place them cut-side down on a large rimmed baking sheet. Roast for 40 to 45 minutes until the flesh is completely tender when you press on the skin and the cut edges have started to caramelize and turn slightly golden. Remove from the oven and let them cool for 10 minutes so they are easier to handle.

While the squash roasts, heat the remaining 1 tablespoon of olive oil in a large saucepan or Dutch oven over medium heat. Add the onion and cook, stirring occasionally, for about 7 minutes until softened and translucent. Add the apple and garlic and cook for another 3 minutes until the apple starts to soften and the garlic smells fragrant. Pour in the vegetable broth, add the cinnamon, nutmeg, salt, and pepper, and bring to a gentle simmer. Cook for 5 minutes, then remove from heat.

Use a large spoon to scoop the roasted squash flesh out of the skin and into the saucepan with the apple and onion mixture. Discard the skins. Stir everything together to combine.

Blend the soup until completely smooth. If using a countertop blender, let the soup cool for 5 minutes first, then blend in batches, filling the blender no more than halfway each time and holding the lid down with a folded towel. If using an immersion blender, blend directly in the pot until no chunks remain, about 2 minutes. The soup should be velvety and smooth with no stringy bits.

Return the blended soup to the pot over medium-low heat. Stir in the apple cider vinegar and taste carefully. Add more salt a pinch at a time until the squash flavor comes forward and the sweetness is balanced. Hot soup almost always needs more salt than you expect. If using cream, stir it in now or swirl a small amount into each bowl just before serving.

Ladle into bowls and serve hot. A drizzle of olive oil, a few pumpkin seeds, or a crack of black pepper on top all make nice finishes for the table.