Roasted chicken with rhubarb

Ingredients

• 1 tbsp olive oil
• 1 tbsp unsalted butter
• 8 chicken drumsticks
• 1 tsp salt
• 1 tsp black pepper
• 2 yellow onions (diced)
• 4 garlic cloves (minced)
• 1.1 pounds rhubarb (chopped)
• 1 tsp grated ginger
• 1 tsp turmeric
• ½ tsp cinnamon
• ½ tsp saffron
• 1 tsp ground cumin
• 1 bay leaf
• 5 tbsp sugar (more to taste)
• 2 tbsp tomato paste
• 1 cup chicken broth
• 1 chili pepper (deseeded and chopped)
• 2 tbsp chopped pistachios
• cilantro (for serving)