Lamb, Lentil, And Rosemary Soup

• 6 lamb stock
• 2 onions
• 2 carrots
• 1 bay leaf
• 1 bone from a roast leg
• 300 gr ripe tomatoes (chopped very)
• 240 gr cubed lamb (cooked)
• 30 ml olive oil
• 14 gr butter
• 3 gr salt