Italian Sausage and Rapini Soup

Ingredients

• 1 medium onion, chopped
• 45 ml (3 tbsp) olive oil
• 300 g (10 oz) hot Italian sausage, in 1 cm / 1/2” pieces
• 1 can, 796 ml (28 oz) Italian plum tomatoes, chopped
• 1 L (4 cups) chicken stock
• 1/2 bunch rapini, trimmed, cut in 5 cm / 2” lengths
• 225 g (1/2 lb) tubetti, cooked al dente, rinsed
• Salt and freshly ground pepper, to taste
• 50 ml (1/4 cup / 25 g) grated Parmesan