Pumpkin soup

Name: Pumpkin soup
Prep time: 10 min
Cook time: 30 min
Total time: 40 min
Cuisine: European
Ingredients: 1 brown onion (approx. 180 g), cut into halves; 20 g butter; 500 g pumpkin, peeled, cut into pieces; 1 carrot, cut into pieces; 500 g water, adjust to taste; 1 tbsp Vegetable stock paste (see Tips); 30 g pouring (whipping) cream (optional); 2 pinches salt, to taste; 2 pinches ground black pepper, to taste; fresh basil, leaves only, for garnishing