Let the chicken get up to room temp before you start and gently pat off any excess moisture with kitchen paper. Pre heat the oven to 300F / 150ºc.
In a bowl, mix 50g of softened butter with the zest of two lemons, 1 garlic clove and the leaves from a couple of sprigs of thyme and 3-4 chopped sage leaves. Leave to one side.
Put a couple of good pinches of salt and cracked black pepper into the cavity of the chicken. Take a lemon and stab it a few times with a fork. Pop the lemon, most of the sage, 8 sprigs of time and 4 garlic cloves (the cloves don't need to be pealed, just lightly bashed) into the cavity.
Using a spoon, gently lift the skin away from the breasts. Be careful you don't pierce the skin. Take the butter mixture and spoon this between the gap you have created between the skin and the breast. use your hands to push this as far down the chicken as you can. Spread any left over butter mixture of the top of the chicken.
In a small pan melt 100g of butter and mix with the juice of two lemons, 1 chopped garlic clove and leaves from a couple of sprigs of thyme and a couple of chopped sage leaves. Once it is all mixed and melted, use the syringe to inject this mixture into the chicken meat. Use about half. **YOU CAN SKIP THIS STEP IF YOU DON'T HAVE A MEAT INJECTOR** Place the chicken, breast side down in a roasting tin, and pop any left over herbs around it, along with slices of lemon and the rest of the garlic cloves. Cover loosely with tin foil and put in the oven.
Roast the covered chicken for 2 hours.
Just before the two hours is up, heat the leftover butter mixture that you used to inject the chicken.
Remove the chicken from the oven and discard the foil. Carefully turn over the chicken so it is breast side up and pour over the melted butter mixture. Place back in the oven for another hour.
To check it's ready, use a meat thermometer which should register at 165F, or check the juices run clear when you pierce the skin. For a super crispy brown skin, place the chicken under the broiler (grill) on medium/high for 5 to 10 minutes, watching closely so it doesn't burn.
Let the chicken sit for 15-20mins, covered, before carving and serving.