Method
Heat the oven to 175°C fan.
Cut the onions in half from root to tip.
Place a large ovenproof frying pan or roasting dish over a medium-high heat. Add half the butter and 1 tbsp olive oil. When bubbling, add the herbs and season lightly.
Place the onions cut-side down in the pan and cook for 4–5 minutes until sizzling, but don’t let the butter burn. Cover loosely with baking parchment and transfer to the oven. Roast for 35–40 minutes until deeply caramelised underneath and very soft.
Remove the onions and set aside. Discard any overly dark herbs.
Place the pan back over a medium heat and pour in the stock, scraping up all the sticky onion juices. Add the oats and stir well. Reduce to a low simmer and cook, stirring frequently, for 4–5 minutes. Add more stock if needed. The consistency should resemble bread sauce.
Stir in the remaining butter, cheese and cream. Season well with salt and pepper.
Spoon into warm bowls and place the roasted onions on top. Serve immediately with extra cheese, crusty bread and a dressed green salad.