I got the inspiration for these sandwiches from an awards dinner I attended where roast beef sandwiches were served on bavarian pretzel buns. I loved the idea, but the dough was way too salty and dry. I wanted a more Auntie Anne's-type bun. So I fooled around a bit, and this is what I came up with. The mustard sauce amounts are estimated, I usually just eyeball it, taste and change. I made these sandwiches at our Christmas and New Year's parties, and now my brother-in-law thinks we should make these every week.