Grate the potatoes and onion in a food processor, fitted with the grating attachment, or with a handheld grater. Place in a clean kitchen towel or cheesecloth and ring out as much of the moisture as you can and then transfer to a large bowl. Add in the egg, breadcrumbs, salt, pepper, and garlic and stir until evenly combined. Allow to rest for 10 minutes.

Preheat oven to 350°F. Place a wire rack over a baking sheet and set aside. Line a plate with paper towels and set aside as well.

Set a large skillet over moderate heat with enough oil to just cover the bottom of the pan. Once hot, add in the potato mixture by large spoonfuls, flattening out slightly. Try not to overcrowd the skillet. Cook until deeply golden-brown, 4 to 5 minutes per side. Adjust the heat if necessary. Drain on the paper towels and transfer to the wire rack to keep from getting soggy. Season with salt while still hot. Continue frying the rest of the potato pancakes until all the mixture is used up.

Meanwhile, to make the dressing, in a large bowl, stir together all of the dressing ingredients until smooth. Cover with plastic wrap and chill in the fridge until ready to use. It can also be made ahead of time and kept in the fridge for up to 5 days.

Cut the Swiss cheese slices in half and top each pancake with one or two halves. Then top with one or two slices of pastrami or corned beef. Bake in the oven for about 5 to 8 minutes or until the cheese has melted. Remove from the oven and top each with dressing and sauerkraut. Serve immediately. Enjoy!