Preheat the oven to 180C/350F/Gas 4.
Season the poussins inside and out with salt and pepper and stuff five garlic cloves and a sprig of thyme inside each bird.
Drape three rashers of bacon over each bird and secure in place with string or toothpicks.
To make the brown chicken stock, preheat the oven to 200C/400F/Gas 6.
Chop the chicken bones with a heavy knife.
Roast them in a roasting tin in the preheated oven for about 30 minutes or until nicely brown. Add the vegetables and roast for another ten minutes.
Transfer the bones and vegetables to a large pan and cover with cold water.
Bring to the boil and skim off any fat and scum. Add the tomato pureé and bouquet garni.
Cover and simmer for two hours, skimming frequently.
Strain through a fine sieve, then store in an airtight container in the fridge for 1-2 days or in plastic bags in the freezer for 2-3 months.
If you want a stronger, thicker stock, you can reduce the stock by boiling, or just thicken it with a little of your favourite gravy thickener.
Place a large ovenproof frying pan in the oven and heat the oil and two tbsp of butter until the butter is foaming and very hot.
Remove the pan from the oven, add the poussins and fry the briefly on all sides.
Place the birds on their sides, return the pan to the oven, and roast the poussins for 15 minutes on each side, with an extra five minutes breast side up to finish.
Remove from the oven, take the birds out of the pan and allow them to rest for five minutes.
Meanwhile pour off excess fat from the pan, then sweat the shallots in the pan with a little of the butter.
Untie the birds and place on a cutting board. Remove the garlic cloves and bacon and set aside on a baking sheet.
Remove the legs and breasts from the poussins and place them on the baking sheets with the garlic and bacon. Keep in a warm place.
Chop the carcasses and the livers if available and add to the shallots. Cook gently for a few minutes.
Add the stock, four sprigs of thyme (reserving a few leaves) and two of the garlic cloves. Simmer for five minutes, then strain through a fine sieve into a clean pan.
Boil until the liquid reduces to a nice sauce consistency (it should coat the back of a spoon). Whisk in the remaining butter and a few of the reserved leaves of thyme, and season with salt and pepper.
Pop the birds back in the oven for two minutes to allow the legs and breasts and garlic cloves to heat through.
To serve, arrange two legs and two pieces of breast on each warm plate. Pour over a little sauce and garnish with the roasted bacon, garlic, and the remaining thyme leaves.
Serve at once with the potato champ.
To make the potato champ, quarter the potatoes. Put them in a large pan of cold, salted water and bring to the boil.
Simmer for 20-30 minutes until the potatoes are just cooked. Pour off the water, cover the pan and let it sit in a warm place for about three minutes. This allows the potatoes to become soft and completely cooked.
While the potatoes are resting, wash and finely chop the spring onions. Combine the milk and four tablespoons butter in a small pan and bring to the boil.
Put the chopped spring onions into the boiling milk, then remove from the heat and leave to infuse for about one minute. This mellows the raw onion taste.
Mash the potatoes and stir in the milk mixture until everything is smooth. Check for seasoning and add salt if necessary.
Serve topped with a generous spoonful of butter with the roasted garlic and thyme poussins.