Make the Russian dressing: In a bowl, mix together all the ingredients.
[Make-ahead: Transfer to a container and refrigerate.]
Make the BBQ brisket sauce: In a small saucepan, combine all the ingredients. Cook over low heat for 30 minutes to thicken and reduce. Remove the bay leaves.
Slice the brisket and combine it with the BBQ sauce.
Make-ahead: Cool and refrigerate.
Night of: Place the brisket and sauce in a skillet, with a splash of stock or water if the sauce is too tight, and reheat gently. Uncover and keep warm over low heat.
Heat a sandwich press or a large griddle over medium heat.
To assemble the sandwiches: Warm the sauerkraut in a small pan. Lightly butter one side of each piece of bread and place the bread buttered-side down. Place a slice of Swiss cheese, folded to fit the bread, on 4 of the slices. Divide the meat among the 4 slices and top the meat with some sauerkraut and another slice of cheese. Slather some of the Russian dressing on the remaining 4 slices of bread and close up the sandwiches, buttered-side out.
Press the sammies in the press until the cheese melts or griddle until deeply golden on both sides. Serve the sandwiches with halved deli pickles and salted radishes.