Preheat the oven to 350°F and line a 9x13 inch baking dish with foil, leaving an overhang on two sides.

Without separating the individual rolls, slice the whole slab in half horizontally so you have a top and bottom layer.

Set the bottom layer in the pan and cover it with the corned beef, then the Swiss cheese, then the sauerkraut if using.

Set the top layer of rolls back on and press down gently to close the sandwich.

Whisk the melted butter, Dijon, brown sugar, Worcestershire, and poppy seeds together and brush the mixture evenly over the tops of the rolls.

Cover the pan with foil and bake for 15 minutes, then uncover and bake 8 to 10 minutes more, until the tops turn deep golden and the cheese fully melts.

Let the sliders rest for 5 minutes, then lift them out using the foil overhang and cut along the roll seams into individual sliders.