ready in 45 min.
Preheat oven to 400º F. Line a baking sheet with parchment paper.
On a lightly floured work surface, carefully unfold both sheets of pastry, Roll each sheet out into a large rectangle, then cut each rectangle into 2 long rectangles. Brush the cut pastry with mustard.
Cut the kielbasa in half lengthwise, so you have 4 long pieces. Place the kielbasa down the middle of each pastry rectangle. Combine the beaten egg and milk and brush the sides and bottom edge with the egg mixture. Fold the pastry over onto the egg-washed edge and press down gently to seal. Trim away any excess pastry.
Lightly score each roll diagonally with a knife. Do not cut through the pastry. Repeat with the remaining pastry and kielbasa. Brush each roll with remaining egg wash.
Place rolls on prepared baking sheet and bake for 20 to 25 minutes or until nicely browned and heated through. Slice and serve immediately with your favorite dipping sauce or mustard.