Thai Pumpkin Shrimp Soup

Ingredients for 5-6 servings:

1/3 cup of self made red curry paste: 2-3 dry red chilli peppers, a 2cm piece of galangal or ginger, 2 shallots, 4-5 gloves of garlic, 1 teaspoon of shrimp paste, 3 stalks of lemongrass, 2 tablespoons of vegetable oil
400ml coconut milk
500gr chicken necks for 1 liter of chicken stock
3-4 kafir leaves
1kg butternut pumpkin, or a mixture of regular and butternut pumpkin
2-3 tablespoons of fish sauce
1 tablespoon of lime juice or lemon juice
800gr shrimps
200gr clamshell or oyster mushrooms
Garnishes: finely chopped green onion, red chili pepper, cilantro, basil, watercress