Persian lamb and rhubarb stew

Ingredients

• 40 gram butter
• 1 kilogram diced lamb
• 1 medium_piece (150g) brown onion, sliced thinly
• 1/4 teaspoon saffron threads
• 1/2 teaspoon ground cinnamon
• 1/4 teaspoon ground turmeric
• 1 cup (250ml) water
• 2 cup (500ml) chicken stock
• 2 tablespoon tomato paste
• 2 3/4 cup (300g) rhubarb, coarsely chopped
• 1/4 cup fresh mint, finely chopped
• 1 1/2 cup (375ml) vegetable stock
• Olive and parsley couscous
• 1 1/2 cup (300g) couscous
• 30 gram butter
• 1 cup (150g) seeded kalamata olives
• 1/2 cup fresh flat-leaf parsley, coarsely chopped