
For the dressing, whisk the ingredients together until smooth. Refrigerate until ready to use.
Heat corned beef in a skillet just until warm, 20-30 seconds.
Warm the sauerkraut in a small pot on the stovetop over low heat (important so the sandwich isn’t cold/wet in the center).
Build the Sandwich. On 4 slices of rye bread, spread the dressing, then add Swiss cheese, warmed corned beef, warmed/drained sauerkraut. Drizzle a bit more dressing, top with another slice of Swiss if you like it extra melty. Top with remaining bread.
Butter the outside of the bread (or spread mayo for extra crispy).
Heat a skillet or large pan to medium heat. Cook each sandwich 3-5 minutes per side, until golden and the cheese melts. Pro Tip: Cover the pan (or tent) to help melt the cheese - a tiny splash of water added nearby creates steam for extra melting power.
Rest 1 minute, slice, and serve hot.