Preheat the oven to 400 degrees F. Line a baking sheet with parchment.
Whisk together the mayonnaise, ketchup, horseradish, onion powder, Worcestershire sauce, hot sauce and a pinch of salt in a small bowl. Season with additional salt if needed. Set aside
Stir the baking soda into 1/3 cup of super-hot tap water until dissolved. Set aside.
Put the sauerkraut into a large kitchen towel and wring it out over the kitchen sink to remove any excess liquid. Set aside.
Sprinkle the dough all over with the caraway seeds then roll into a 20-by-14-inch rectangle on a lightly floured work surface. Some of the caraway seeds will fall away from the dough, but a lot of the seeds should work in as you roll it out. Arrange the pastrami evenly on one half of the dough, starting on the shorter end and leaving a 1-inch border on the sides. Spread half the sauce over the pastrami. Separate the cheese pieces and shingle them over the sauce. Scatter the sauerkraut on top. Working from the short side, tightly roll up the dough into a log, jelly roll-style. Pinch the open ends together to seal, then tuck them underneath the log.
Transfer the log, seam side-down, onto the prepared baking sheet and brush all over with the baking soda wash (you will not use all the wash). Bake, rotating the pan halfway through, until the bread is deep golden brown, 40 to 50 minutes.
Let the bread cool for 10 minutes. Slice into 8 pieces and serve warm with the remaining sauce.
To make rolling and shaping the dough easy, keep the dough refrigerated until 10 to 15 minutes before you are ready to use it.
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