Thoroughly dry each chicken breast with a paper towel.
In a small bowl combine olive oil, salt, Italian seasoning, paprika, garlic powder, onion powder, and black pepper.
Brush the seasoning paste on both sides of each chicken breast.
Add chicken stock to a 6-quart slow cooker. Add chicken in a single layer in the pot. Place rosemary and thyme on top, if using.
Cover and cook on the "Low" setting for 1 1/2 to 2 1/2 hours. Cook until the internal temperature reaches 160 to 165ºF (71 to 74ºC). An 8-ounce breast takes about 2 hours.
Transfer chicken to a plate or carving board. Loosely cover to keep warm while making the gravy.
Transfer chicken drippings in the slow cooker to a measuring cup. Add additional chicken stock until the volume reaches 1 cup.
Heat a medium-sized pan over medium heat. Melt the butter and then whisk in flour. Whisk and cook until a pale yellow roux forms, about 1 to 2 minutes.
Gradually whisk in the drippings. Turn the heat up to medium-high, continuously stir until thickened, about 1 to 2 minutes. Add more chicken stock if desired to thin the sauce. It will thicken more as it cools—season gravy with salt and pepper. If desired, strain the gravy for a smoother sauce.
Storing: Cool completely and store refrigerated in an airtight container for up to 7 days. Freeze for up to 9 months.
Make it Gluten-Free: Substitute cassava flour or cornstarch for all-purpose flour. If using cornstarch, dissolve 1 tablespoon in 2 tablespoons of water. Add to chicken stock and then stir and cook on the saute function until the liquid thickens.