Cut squash in half and scoop out guts, reserve seeds for pepitas if desired.
Coat open face of squash with oil and roast at 350°F skin side up on a baking sheet liberally coated with non stick spray, until a paring knife gives little resistance when gently pushed through the largest part of the squash (about 45-75 mins, depending on size of squash).
(Check squash at 35 mins, and in 20 min intervals following.).
Put fresh herbs in cheesecloth so they are easy to remove later.
Chop celery and onions.
In a large saucepan, stock pot, or instant pot, sautee celery and onions in butter with fresh herbs until cooked through. Add 1 tsp salt and pepper to taste.
Remove herbs from celery and onions.
Add vegetable stock to cooked celery and onion mix. (Keep on low until squash is roasted).
Remove squash from oven and allow to cool for 15 mins.
Scoop squash from peel and place in stock with celery and onions.
Use immersion blender until smooth.
(If you don’t have an immersion blender, a stand blender will work, but requires a bit more work and a second pot to transfer your soup to. Blend squash into soup 1/3 at a time, and transfer all soup to one pot. Pot to blender to pot back and forth, until soup is smooth and consistent.).
Add 1/2 cup of half and half.
Cook for at least 90 minutes.
Serve with a tsp of heavy whipping cream in the center of the bowl, and top with a few pepitas.
Pepitas: thouroughly rinse and clean seeds from squash. Lay flat on a foil lined baking sheet liberally coated with non-stick spray. Salt and pepper to taste. Roast at 350°F for 15-20 mins or until golden brown.