Remove and discard any packaging and netting from the turkey breast.
Place the thawed turkey breast in the bottom of a 4 quart crock pot, skin side up.
Add the chicken broth.
Spread the minced garlic over top of the turkey.
Sprinkle salt and fresh cracked black pepper over top.
Cut the onion into rings and layer on top of the turkey.
Cover and cook on low for 8 hours and do not open the lid.
Pre-heat the oven broiler.
Leave the onions and broth in the crockpot and carefully remove the cooked turkey to a broiler pan, skin side up. Broil for about 5 - 7 minutes or until lightly browned. Watch it closely so it doesn't burn.
Turn the crockpot to high heat.
Add butter to the broth stir until melted. Whisk together cornstarch and water until a smooth slurry forms, and then whisk into the turkey drippings.
Simmer 15 minutes whisking occasionally.