Preheat the oven to 200°C.
Place chopped onions and carrots in a roasting tin and set the chicken on top.
Season with salt and pepper, drizzle with oil, and add 75ml of water to the tray.
Roast for 60 to 75 minutes until cooked through.
Remove the chicken from the oven and rest for 10 minutes under a cover.
Boil 37.5g of butter and 200ml of water in a saucepan.
Add asparagus, peas, shallot, and marjoram then simmer for 4 minutes.
Drain the vegetables and stir in the remaining 37.5g of butter.
Carve the meat and serve alongside the vegetable fricassée.