Curried cauliflower soup

Ingredients

• 2 tablespoon olive oil
• 2 tablespoon butter
• 1 large onion, coarsely chopped
• 4 clove garlic, peeled and chopped
• 2 tablespoon medium-heat curry powder
• 400 gram (2 large) floury potatoes, peeled and coarsely chopped
• 4 cup chicken stock (or vegetable stock, if preferred)
• 600 gram (1 small) cauliflower, trimmed and coarsely chopped
• 1/2 cup sour cream
• salt and freshly ground black pepper
• 1/4 cup chopped fresh coriander or parsley