• If starting from frozen, a 6-8 lb turkey breast will take about 2-3 days to fully thaw in the fridge. Place it on a tray or in a pan to catch any drips, and plan ahead so it has time to thaw completely before cooking.
• Place the celery, onion, and carrots in the bottom of the slow cooker, spreading them out in an even layer. Pour the chicken broth over the vegetables.
• In a small bowl, stir together the melted butter, garlic powder, paprika, thyme, sage, salt, and pepper until combined into a paste.
• Pat the turkey breast dry with paper towels. Gently loosen the skin from the meat with your fingers, being careful not to tear it, to create a pocket.
• Spread the butter mixture evenly under the skin, directly onto the meat, then rub any remaining mixture over the outside of the skin.
• Place the turkey breast on top of the vegetables in the slow cooker, skin side up.
• Cover and cook on low for 5-6 hours, until the internal temperature reaches 165°F at the thickest part of the breast.
• Carefully remove the turkey breast from the slow cooker and let it rest for 10-15 minutes before slicing. Pour the juices from the slow cooker over the meat to add moisture.

For the gravy:

• Strain the reserved slow cooker liquid through a fine mesh strainer into a measuring cup or bowl, discarding the solids.
• In a medium saucepan, melt 3 tablespoons of butter over medium heat. Whisk in 3 tablespoons of flour and cook for 1-2 minutes, until golden.
• Slowly pour in the strained liquid (2-2 ½ cups depending on preference for consistency), whisking constantly to prevent lumps.
• Bring to a simmer and cook for 4-5 minutes, whisking occasionally, until the gravy has thickened to your liking. Season with salt and pepper to taste.