1 Preheat the oven to 200°C. Remove the stalks from the mushrooms and chop finely.
2 Melt the butter in a small pan and add the onions. Cook gently for 5 minutes.
3 Add the mushroom stalks, garlic and thyme and cook for a further 2 minutes.
4 Top the whole mushrooms with the filling, and cook in the preheated oven for 15 minutes.
5 Top each mushroom with a Camembert half and cook for a further 5 minutes.
6 Halve the burger buns and spread with mayonnaise. Place a filled mushroom and top with rocket leaves and the bun lids. Serve immediately.