Preheat the oven to 170°C.
Peel the onion and cut into thick wedges. Slice the carrots lengthways. Peel the parsnips and potatoes then cut into chunks.
Put the olive oil into a roasting tin, coat the vegetables in it then place the bird on them.
Rub the butter into the skin and season all over. Place the bacon rashers evenly over the bird, then roast for 35 minutes.
Take out the tray, put the bird to one side. add the garlic & thyme, give a good stir then pour over the cider and stock. Put back in the oven for another 35 minutes.
Take out the guinea fowl to rest - cover with foil to keep warm. Increase the temperature to 190°C, stir the veg and let them bake for another 10-15 minutes.
Take the vegetables out, put them with the bird and cover. Sprinkle the cornflour over the jus in the tray, stir in well then put over a low flame on the hob continuing tto stir for a few minutes until it thickens.
Carve the bird, plate up with the vegetables and pour over the gravy. Bon appétit!