I start by patting the turkey breast completely dry with paper towels, since a dry surface helps the seasoning stick better and the skin crisp up later. If it was frozen, make sure it's fully thawed in the fridge first, which usually takes a day or two depending on size. I also trim any excess fat so the seasoning touches more of the meat directly.
In a small bowl, I mix the softened butter with garlic powder, onion powder, thyme, sage, paprika, salt, and pepper until it forms a smooth paste. This step only takes a minute, but it's what gives the turkey most of its flavor, so I don't skip it even when I'm in a hurry.
I place the carrots, celery, onion, and garlic in the bottom of my crockpot so the turkey sits above the liquid rather than soaking in it. This little trick is what keeps the skin from turning soggy during the long cook time. Then I pour the chicken broth around the vegetables, not over the turkey.
Next, I rub the butter mixture all over the turkey breast, getting under the skin a little if I have time, since that's where the flavor really sinks in. I set the breast skin-side up directly on top of the vegetable bed. This positioning helps the turkey cook evenly while staying protected from the broth below.
I cover the crockpot and cook on LOW for 5 to 6 hours or on HIGH for 3 to 4 hours, depending on how much time I have that day. Around the last hour, I start checking the internal temperature with a meat thermometer inserted into the thickest part of the breast. I'm looking for it to reach 165°F before I even think about pulling it out.
If I want crispier skin, I carefully transfer the turkey to a baking sheet and broil it for 5 to 6 minutes until golden. This step isn't required, but it adds a nice texture contrast to the otherwise tender meat. Just keep a close eye on it so it doesn't burn under the broiler.
Once it's out of the oven or crockpot, I let the turkey rest for about 15 minutes before slicing, which keeps all those juices locked inside instead of spilling onto the cutting board. While it rests, I strain the vegetables and broth, whisking in a little flour over heat to make a quick gravy. Then I slice the turkey against the grain and serve it warm with the gravy on the side.