Step 2
Make sure the turkey breast is dry and cover the top and sides with the spice rub. Loosen the skin slightly and spread some of the spice rub below the skin as well.
Step 3
Place the onion, celery stalks, and carrots in the bottom of the slow cooker to form a bed for the turkey breast. Set the turkey breast on top so it isn’t touching the bottom of the slow cooker.
Step 4
Cover and cook on low for 3-4 hours on low (see notes) or until the turkey has reached an internal temperature of 165 degrees. For a really juicy turkey, take it out around 160 degrees since it will continue to cook as it rests. Bone-in turkey breasts will take closer to 6 hours. Let rest for 15 minutes before slicing or serving.
Step 5
For crispy skin: Preheat the broiler to high heat and the baking rack about 10-12 inches from the heat source. Place the turkey on a sheet pan covered with foil. Broil for 3-5 minutes until skin is browned and crispy. Keep a close eye so it doesn't burn.
Step 6
Optional gravy: Melt 2 tablespoons of butter over medium heat in a pot. Once melted, add 2 tablespoons of flour to make a roux. Whisk together and cook for 1-2 minutes until flour is fully incorporated and light brown in color. Add 1 cup of the strained cooking liquid from the slow cooker. Continue to whisk and cook until it thickens. This normally takes about 5 minutes. Taste and season as needed.