Trim the bottoms from the Brussels sprouts and remove any dry leaves from the outside. Cut them in half through the stem if they are very large.
Place the Brussels sprouts in the slow cooker. Add the butter, mustard, maple syrup, broth or water, salt, and pepper, as well as the cayenne if using. Stir well to coat the Brussels sprouts with the sauce.
Cover and cook on high for 2 hours or low for 4 hours. Stir to redistribute the glaze, and serve hot.
Notes
These can either be cooked on high for 2 hours, or on low for 4 in the slow cooker. If you are having a holiday meal, then you may love these in particular for their ability to free up some oven and stovetop space.