Add oil to a small saucepan. Once hot, add the onion and salt and cook over low heat, stirring frequently for about 1 hour until the onions caramelize.

Preheat oven to 375 degrees Fahrenheit.

Mix truffle mayo with horseradish sauce and spread evenly over the pastry sheet.

Place turkey slices evenly on pastry sheet.

Spread onions across the lower third of the turkey slices. Keeping it thinner at the top will make it easier to roll up the deli roll.

Sprinkle 1/4 tsp of caraway seeds on top of the turkey and onions.

Starting from the bottom, roll up the puff pastry sheet.

Place seam-side down on a greased sheet pan and brush the deli roll with the egg. Cut slits across the top the deli roll. Sprinkle with remaining caraway seeds.

Bake for 35 minutes until golden brown.