Ingredients
For the soup:

1 medium yellow onion, chopped (about 1 cup)
1 celery rib, chopped (about 3/4 cup)
1 carrot, chopped (about 3/4 cup)
2 tablespoons unsalted butter
1 butternut squash, seeded, peeled, and chopped (6 to 8 cups), see How to Peel and Cut a Butternut Squash
1 large tart green apple, peeled, cored, chopped (squash to apple ratio should be 3:1)
3 cups chicken stock or vegetable stock
1 cup water
Pinch nutmeg
Pinch cinnamon
Pinch cayenne
Salt and pepper to taste

For the garnish (optional):

Fresh parsley, chopped
Chives, chopped
Dash smoked paprika
Sour cream

Method
1. Sauté the onion, carrot, and celery in butter:
Heat a large thick-bottomed pot on medium-high heat. Melt the butter in the pot and let it foam up and recede. Add the onion, carrot, and celery and sauté for 5 minutes. Lower the heat if the vegetables begin to brown.

2. Cook the soup:
Add the butternut squash, apple, stock, and water. Bring to boil. Reduce to a simmer, cover, and simmer for 30 minutes or so, until the squash and carrots have softened.

3. Purée the soup:
Use an immersion blender to purée the soup, or work in batches and purée the soup in a stand blender.

Add the seasonings:
Add pinches of nutmeg, cinnamon, and cayenne. Add salt and pepper to taste.

Garnish with chopped fresh parsley or chives and, if you want, a dollop of sour cream.