Step 1: Begin by caramelizing the onions. In a large skillet, melt the butter over medium-low heat. Add the thinly sliced onions and 1/2 teaspoon of salt. Cook slowly, stirring frequently, for 20-30 minutes until the onions are deeply golden brown, sweet, and soft. Remove from heat and set aside.
Step 2: While the onions are caramelizing, prepare your sauerkraut. Drain it thoroughly, pressing out as much liquid as possible with a clean kitchen towel or paper towels. This is crucial to prevent your rolls from becoming soggy.
Step 3: Preheat your oven to 375°F (190°C). Lay the tortillas or flatbreads on a clean work surface. Spread a thin, even layer of Dijon or spicy brown mustard over each tortilla, leaving a small border around the edges.
Step 4: Arrange the pastrami slices over the mustard on each tortilla. Overlap them slightly to cover most of the surface. Ensure the pastrami is evenly distributed without over-piling.
Step 5: Evenly distribute the drained sauerkraut over the pastrami layer on each tortilla. Follow this with a spoonful or two of the caramelized onions.
Step 6: Sprinkle approximately 2 tablespoons of shredded Swiss cheese over the sauerkraut and onion mixture on each tortilla. This cheese will help bind the filling together when melted.
Step 7: Tightly roll up each tortilla from one side, creating a compact log. Ensure the filling is snug inside. Place the rolls seam-side down on a baking sheet.
Step 8: Bake in the preheated oven for 10-15 minutes, or until the tortillas are golden brown and slightly crispy, and the cheese is thoroughly melted and bubbly. For extra browning, you can lightly brush the tops with a little melted butter before baking.
Step 9: Remove the pastrami sauerkraut rolls caramelized onion wrap from the oven. Let them cool for a minute or two before slicing into halves or thirds, or serve them whole.
Step 10: Garnish with fresh parsley if desired, and serve immediately with extra mustard or a side of Russian dressing for dipping. Enjoy your delicious pastrami sauerkraut rolls caramelized onion wrap!