The following recipe was adapted from Daniel Rose's which can be found here. It was also my first time making soup with just water and skimmed milk (instead of stock). Nonetheless the soup was sweet, light and delicious.
2 Tbsp olive oil
1.5 yellow onion, diced
1 large butternut squash, peeled, deseeded & cut into 1-inch chunks
1 large acorn squash, peeled, deseeded & cut into 1-inch chunks
1.5 cups skimmed milk
3.5 cups water
Salt & pepper
1. Heat the olive oil over medium-high heat. Add the onions and saute until softened.
2. Add both squashes and mix them evenly. Let them sit around for about 5 minutes, turning only twice.
3. Add the milk and water. Stir thoroughly.
4. Close and lock the pressure cooker lid. Wait for the pressure indicator to rise and then reduce to moderately low heat. Pressure cook for 15 minutes.
5. Use the immersion blender to puree the soup but stop before it gets too smooth. The texture gets quite dull if it is too smooth.
6. Add salt and pepper to taste.
This yields at least 4 quarts. As suggested by Mr Rose, serve with sauteed porcinis or smoky creme fraiche garnish. The husband likes it with just toasted lightly buttered olive bread.
After the soup has completely cooled, portion them in good ziplock bags for freezing while keeping two servings in the fridge for the day after.