This is from a recent Pillsbury cookbook. I used the beer instead of the apple juice and strained the mustard seeds from the gravy before serving. Great dinner!
Spray a 3 1/2 to 4 quart slow cooker with cooking spray.Place beef roast in slow cooker.
In small bowl, mix mustard, horseradish sauce and gravy mix. Spread mixture over roast. Pour beer around roast.
Cover. Cook on low heat setting 9 to 10 hours.
Remove roast to serving platter; cover to keep warm.
In 2 quart sauce pan mix water and flour until smooth. Pour cooking juices from slowcooker into sauce pan. Heat to boiling over medium-high heat, stirring constantly.