Note Butternut squash should be peeled and seeded and cut into 1 1/2-inch chunks. Leeks use the white and green parts. You can use regular stock in place of the water and omit the veggie stock powder. Also note that it can be any type of stock powder. Chicken would work best. You can add up to 3 tsp sherry vinegar or balsamic vinegar If you like, stir in a tablespoon of basil or rosemary olive oil at the end for added flavor depth. I used basil.
Finely chop squash. A food processor works well here. You should have 5 cups. Finely chop celery. Set aside with squash.
Heat 2 tbsp of water and saute the leeks for 1 minutes. Note you can also use the basil olive oil for this if you are not keeping fat free. Saute the leeks for 1 minutes.
Add the water and stock powder or add the stock and bring to a boil over high heat. Stir in squash, celery, oats, Herbes de Provence and salt then return to boil. Reduce the heat to medium, cover and cook at gentle boil until squash is soft. About 15 minutes.
Puree the soup with an immersion blender[I use the Phillips. works fine] or cool slightly and transfer in small batches to food processor or blender and blend until smooth and creamy.
Stir in enough vinegar to heighten the flavors. Adjust salt if needed, and reheat if necessary. Garnish with the chives.
From recipe "Cooking under pressure: After the initial sauté, cook all the ingredients in a pressure cooker for 4 minutes under high pressure. Use a quick-release method or allow the pressure to come down naturally. Proceed as directed in the recipe.".