In a small bowl, place the softened butter, lemon zest, salt, pepper, garlic powder and thyme and mash butter with a fork until all the ingredients are combined.
Peel and quarter the onions. In a large baking dish, break up the onion wedges and cover the bottom of the baking dish.
Pat the turkey dry all over with a paper towel.
Sprinkle some of of the extra salt inside the turkey cavity.
Place the turkey breast side up on top of the onions in the baking dish.
Cover the skin of the turkey breast all over with the softened butter mixture.
Pour the chicken stock into the bottom of the baking dish.
Cover the turkey with foil, try not to have the foil touching the top of the turkey.
Place turkey in oven and cook for 40 minutes. After 40 minutes, remove from oven and baste the breast in the pan juices. Place back in oven for a further 40 minutes. Remove again and baste. Remove foil and place back in oven uncovered for a further 40 minutes.
Once turkey is cooked remove from oven. You can check it is cooked by using a meat thermometer. Insert the thermometer into the thickest part of the meat. You are looking for a temperature of at least 74C/165F. The juices coming from the turkey will be clear if it is cooked through.
Remove turkey from the baking dish and place on a large plate. Cover with foil and allow to rest for 30 minutes. While the turkey is resting, prepare the cherry sauce. You will need the pan juices so don't discard them.
Drain the juices from the pan through a sieve into a small saucepan. Place the onions aside and keep warm for serving.
Bring the pan juices in the small saucepan to a boil, and reduce to a simmer for 10 minutes to reduce the liquid.
Add the cherry jam and bring the liquid back up to a boil. You may need to increase the heat for this. Simmer the sauce for 2-3 minutes. Taste the sauce at this point, you may need to add salt if required.
At this point, if the sauce is very thin, you may need to use xanthan gum to thicken. If so, remove from the heat and lightly sprinkle ¼ tsp of xanthan gum and stir. Allow sauce to sit for 1-2 minutes and see if it thickens. You can use another ¼ tsp of xanthan gum here if still too thin. (Be careful using the xanthan gum. If you use too much the texture of the sauce will become slimy.)
Once the turkey is rested and the sauce is made, carve the turkey and serve with the onions and the sauce.