Cauliflower and cheese bake with onion rings

Ingredients

• 1 small cauliflower, outer leaves removed, broken into florets
• 1 medium red onion, peeled
• 5 tbsp olive oil
• ½ tsp finely chopped rosemary
• 7 eggs
• ½ cup basil leaves, chopped
• 120g plain flour, sifted
• 1 ½ tsp baking powder
• 1/3 tsp ground turmeric
• 150g coarsely grated Parmesan
• Melted unsalted butter
• 1 tbsp white sesame seeds
• 1 tsp nigella seeds
• Salt and black pepper