Lamb tajine and carrots

Ingredients :

 2 bay leaves
 2 cloves of garlic
 1 teaspoon cinnamon
 1 teaspoon of cumin
 1/2 lemon
 1 kg of lamb cut into 8 pieces (necklace)
 50g of blond dried grapes
 600g carrots
 2 large onions
 2 saffron pods
 2 tablespoons of olive oil
 20g butter
 salt, pepper