Preheat oven to 400°F; prepare a baking pan with parchment or cooking spray.
Lightly flour a clean, dry surface; roll out puff pastry to ~⅛ -inch thick; cut in six equal rectangles.
Mix mustard and mayonnaise; brush pasty with mixture within¼ -inch of edges. Brush pastry edges with whisked egg.
Roll pastry around sausage; pinch seam and ends well to seal; turn seams to down side.
Brush tops and sides of each roll with egg; sprinkle each with poppy seeds, if desired.
Cut rolls into 1½-inch pieces.
Transfer each to baking sheet; bake ~20 minutes, until golden brown.
