Directions
Lay the chicken breasts in an even layer across the bottom of a 4 to 6 quart slow cooker. They can overlap very slightly if needed, but try to keep them in a reasonably single layer so they cook evenly and shred easily when done.
In a medium mixing bowl, whisk together the honey and Dijon mustard until the two are completely smooth and thoroughly combined. The mixture will be thick, glossy, and deeply golden with the distinctive speckled appearance of Dijon mustard throughout. Take a moment to whisk it properly so the honey and mustard are fully integrated rather than separated.
Pour the honey mustard mixture evenly over the chicken breasts in the slow cooker. Use a spoon or a pair of tongs to turn each piece of chicken once or twice so that both sides are well coated in the sauce. You want the chicken to be generously covered so it can braise in the sauce throughout the cooking time rather than drying out on top.
Place the lid securely on the slow cooker and set it to LOW. Cook for 4 to 5 hours on LOW, or alternatively on HIGH for approximately 2 and a half to 3 hours, until the chicken is completely cooked through, very tender, and can be pulled apart easily with two forks. The cooking time may vary slightly depending on the size and thickness of your chicken breasts and the particular slow cooker you are using, so check for tenderness at the lower end of the time range and add more time if needed.
