Preheat the oven to 200C/400F/Gas 6.
For the spatchcocked chicken, place the chicken, breast-side down, onto a chopping board. Using good kitchen scissors cut through the flesh and bone along both sides of the backbone from the tail end to the head end and completely remove the backbone. Place the chicken, breast-side down, onto a roasting tray and press it down as flat as possible. Once the chicken is flattened out, turn it breast side up in the roasting tray.
Mix the maple syrup, lemon juice, mustard and thyme leaves in a bowl until well combined. Season the chicken, to taste, with salt and freshly ground black pepper then, using your hands, slather the maple syrup mixture over the skin of the chicken.
Transfer the spatchcocked chicken to the oven to roast. At the same time, place the garlic bulb from the Caesar salad, in its foil, into the oven with the chicken for about 20 minutes, or until the garlic is very soft. Remove the garlic from the oven and set aside to cool. Continue to roast the chicken for a further 25 minutes, or until crisp, golden-brown and cooked through. (The chicken is cooked through when the juices run clear when a skewer is inserted into the thickest part of the chicken.) Remove the spatchcocked chicken from the oven and rest for 5-10 minutes before serving.
When the garlic bulb is cool enough to handle, remove the foil and squeeze the roasted garlic into a small food processor.
Add the white wine, Chardonnay vinegar, mustard, egg yolks, Worcestershire sauce and parmesan to the food processor and blend to a fine purée. Gradually add the rapeseed oil in a slow steady stream, blending continuously, until the dressing thickens and emulsifies. Season, to taste, with salt and freshly ground black pepper.
Mix the bread cubes in a bowl with the olive oil, rosemary, salt and freshly ground black pepper until well coated. Fry the bread cubes, in batches, in a frying pan over a high heat for 2-3 minutes, turning frequently, until golden-brown and crisp.
To serve, carve the chicken into pieces and divide among 4-6 plates. Mix the romaine lettuce with the hot crôutons and a drizzle of Caesar dressing, then pile immediately onto the plates alongside the chicken. Add more dressing to taste.