Preheat the oven to 400°. In a small bowl, stir together the egg whites and milk.
Separate the dough into 8 triangles and, using a rolling pin, roll them out on a floured surface. Starting at a pointed corner, roll up 1 sausage in each triangle. Smooth the seams together with a bit of the egg white mixture.
Brush the dough with the egg white mixture; roll in the poppy seeds. Trim off a sliver from each dough-covered end and discard. Slice each sausage crosswise into 6 rounds; arrange on 2 parchment-lined baking sheets. Bake until golden, 12 minutes. Insert a skewer into one end and serve with the mustard.