Pat roast dry. With tip of sharp knife, make 24 evenly spaced slits in beef, about 1/2 inch deep. Quarter garlic cloves lengthwise; insert 1 into each slit. Set aside on greased rack in small roasting pan.
In small bowl, stir together mustard, vinegar, oil, soy sauce and hot pepper sauce; brush evenly over beef, reserving any remaining mixture. (Make-ahead: Cover beef and mustard mixture and refrigerate separately for up to 1 day.)
Pour enough water into roasting pan to come 1/2 inch up side. Roast in 500°F oven for 30 minutes. Remove from oven. Brush with reserved mustard mixture. Reduce temperature to 275°F; roast until meat thermometer registers 140°F for rare, about 40 minutes, or 150°F for medium-rare. Transfer to cutting board. Tent with foil; let stand for 20 minutes before slicing thinly across the grain. (Make-ahead: Let cool completely in refrigerator; cover and refrigerate for up to 2 days. Reheat, moistened with a few spoonfuls of beef stock or dip.)
Meanwhile, skim fat from pan juices. Pour in wine; bring to boil over high heat, stirring to scrape up any brown bits from bottom of pan. Boil until reduced by half, about 5 minutes. Pour in stock and return to boil; boil hard until reduced to about 2 1/2 cups, about 15 minutes.
Cut baguette in half lengthwise. Cut into 8 sandwich-size portions. Drizzle about 1 tbsp dip onto cut sides of bread, or spread with mustard (if using). Pile beef on bottom baguette slices; top with remaining baguette, pressing to sandwich. Serve each sandwich with 1/4 cup juices in small bowl for dipping.