Dice 200g mushrooms, trim remaining 800g and set aside. Heat oil and 60g butter in a frying pan over medium heat. Add onion, cook, stirring for 5 minutes or until soft. Increase heat to high, add diced mushrooms and cook 5 minutes until golden. Set aside to cool. Transfer to a large bowl add breadcrumbs, pistachios, ? cup craisins and 1 tablespoon thyme leaves. Season to taste, mix until well combined.
Preheat large roasting pan and oven to 220°C or 200°C fan forced. Loosely fill spatchcockcavities with stuffing. Tie the legs together and brush both sides with remaining butter.
Scatter trimmed mushrooms and remaining thyme over base of hot pan. Nestle spatchcocks in between mushrooms and roast for 45 minutes. Remove from oven. Increase oven to 250°C or 230°C fan forced.
Remove spatchcocks to aclean pan and roast a further 5-10 minutes until golden and cooked through. Toss the spinach leaves and remaining craisins with roasted mushrooms and serve with spatchcocks.