Heat oven to 400° F. Mix 5 tablespoons of the Kerrygold Pure Irish Butter, garlic, and thyme in a bowl with a spoon until soft. Carefully, using your fingers, peel the skin away from the chicken breast and rub the butter mixture under the skin. Rub the outside of the skin with the canola oil and season with the salt and pepper.
Stuff the cavity of the chicken with the lemons, rosemary and garlic head. Place the chicken in a roasting pan and roast 1 hour or until juices from the thigh run clear when pricked with a knife. Remove from oven and let chicken rest on a platter while you make the gravy. Put the roasting pan on a burner over low heat, sprinkle in the flour, and stir to incorporate any liquid in the pan. Gradually add the chicken stock, stirring constantly. Transfer the gravy into a small pot, and simmer over low heat until it has the preferred consistency. Add additional salt and pepper to taste and whisk in remaining 1 tablespoon of butter; strain the gravy through a fine mesh sieve before pouring it onto the chicken (which will have released some juice onto the plate by now).