In a large slow cooker, combine broth, Worcestershire sauce, mustard, coriander seeds, and brown sugar.
Rinse the corned beef briefly with water. This will reduce the amount of salt. Place corned beef in slow cooker .
Place peeled and cut carrots in cooker around the meat. Then top the meat and carrots with chopped green cabbage. Set slow cooker to low and cook for 8 hours.
Horseradish Mustard Sauce
Melt butter in a small sauce pot and then whisk in flour. Next add in horseradish and mustard.
Pour in milk and cook on low until sauce thickens. Add more milk if sauce is too thick. Salt to taste.