Preheat the oven: preheat the oven to 180°C / 350-375°F / Gas Mark 4-5.
Seasoned butter: add the butter, garlic powder, onion power, salt and pepper to a small mixing bowl and use a rubber spatula to stir until consistently combined.
Chicken: remove the packaging from the chicken, place it onto a clean, dry cutting board and use a folded piece of paper towel. to pat it dry.
Butter mixture: use the spatula to coat the chicken with the butter mixture. Gently pull the top skin to insert some under there also above the cavity. Then use your hands to massage the seasoned butter into the chicken, across the legs, thighs and wings.
Stuff: insert the lemon, both halves of the garlic head, rosemary, thyme and bay leaf into the cavity of the chicken and then use kitchen string to tie the legs together. Once done, transfer the chicken to a large baking dish.
Oil and bake: drizzle the olive oil over the chicken and gently spread to evenly coat the chicken. Then place the baking dish into the preheated oven on the middle shelf. Bake the chicken for 1 ½ hours and then use a thermometer to check the temperature. We are aiming for the chicken to reach an internal temperature of 74°C (165°F). Oven times will vary slightly. Note 4
To serve: once you have checked that the temperature is right and the chicken is cooked through, use oven mitts to place the roasting pan on a heatproof surface. Then let the chicken rest for 10-15 minutes. Once rested, carve the chicken and serve it with roast potatoes, lemon wedges and gravy or sauce.