Combine pork, potato, onion, parsley, sage, salt, pepper, and pepper flakes in bowl; transfer sausage mixture to bag.
Unfold 1 pastry sheet; following fold marks, cut each sheet into 3 rectangles. Cut each rectangle in half lengthwise to make 6 strips. On a lightly floured surface, roll out each strip into 12 x 2 1/2-inch rectangle. Pipe sausage mixture along 1 long edge of each strip. Lightly brush opposite edge with egg. Starting at edge with sausage mixture, roll up each strip, gently pressing egg-brushed edge to seal.
With a sharp knife, cut each log crosswise into 8 (1 1/2-inch-thick) rolls. Arrange rolls, seam side down, on a broiler pan; brush top with egg. Repeat with remaining pastry and sausage mixture.
Bake until golden and cooked through, about 30 to 35 minutes. Serve warm with Worcestershire sauce for dipping.