Make the mustard. In a small bowl, combine the mustard and vinegar and mix well. Cover with plastic wrap and let sit overnight at room temperature to develop the flavors.

In a small saucepan over low heat, add the mustard, honey, and egg yolks. Cook, whisking constantly, until thickened, 7 minutes. Cool, then refrigerate until ready to serve.

When ready to cook, set Traeger the temperature to 350°F and preheat with the lid closed for 15 minutes.

In a medium bowl, thoroughly combine the sausage and onion.

On a lightly floured work surface, roll each sheet of puff pastry, (there are two to a package), into an 11-inch by 10 ½-inch rectangle. Using a pizza cutter or knife, cut each rectangle widthwise into three strips, each 3-½ inches wide.

With wet hands, mold some of the sausage into a tube-like shape.

Place the sausage in the center of one of the puff pastry strips. Wrap the pastry around the sausage and seal the seams with a bit of beaten egg. Repeat with the remaining sausage and puff pastry.

Place the rolls seam-side down on your work surface, and brush the tops lightly with the egg.

Cut the rolls into pieces about 1 ½-inches long and transfer to a rimmed baking sheet lined with parchment paper, leaving about an inch between each roll.

Place the baking sheet directly on the grill grates. Close the lid and bake until the sausage is cooked through and the pastry is golden brown, 25 minutes.

Remove the sausage rolls from the grill and serve hot with the honey mustard. Enjoy!