Fontina, Pecorino & Leek Soup (Zuppa di Formaggi e Porri)

Ingredients

• 50 gm butter, coarsely chopped
• 2 tbsp olive oil
• 3 leeks, thickly sliced widthways (1cm thick)
• 4 garlic cloves, finely chopped
• 1 litre (4 cups) chicken stock
• 4 thick slices day-old ciabatta
• 160 gm Fontina, sliced
• 160 gm finely grated pecorino
• To serve: oregano leaves