Curried cauliflower soup

Ingredients

• 2 tablespoons olive oil
• 2 tablespoons butter
• 1 large onion, coarsely chopped
• 4 cloves garlic, peeled and chopped
• 2 tablespoons medium-heat curry powder
• 400 grams (2 large) floury potatoes, peeled and coarsely chopped
• 4 cups chicken stock (or vegetable stock, if preferred)
• 600 grams (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