On a floured surface spread out one puff pastry sheet, making sure its length matches that of the tenderloin, rolling if necessary then cut in half lengthwise. Divide apple/onion mixture in quarters and spread 1/4 each on the 2 pastry layers (saving the other half for the remaining pork and pastry). Slice the havarti cheese thinly and layer slices over the apple/onion mixture. Finally lay the tenderloin lengthwise on one long edge and wrap it up like a jelly roll. Seal the seam with the egg/water mixture then brush the rest over the pastry. Repeat with the remaining tenderloins then gently slice them into sections about 1 in. (2.5 cm) thick. Cover two large baking sheets with parchment paper then lay the sections on them. Either bake at 400°F (200°C) for about 15 min. or keep in the fridge for a couple of hours and bake just before serving.