Preheat the oven to 375°F (190°C). Lightly grease an 8x8-inch baking dish.

Drain the sauerkraut thoroughly and squeeze out excess liquid. Combine the sauerkraut and Thousand Island dressing in a bowl.

Separate the crescent dough into two equal halves. On a lightly floured surface, press and seal the perforations to form a seamless sheet.

Roll one half to about a 12-inch square. Fit it into the prepared baking dish so it covers the bottom completely. Trim any overhang.

Bake the bottom crust for 8–10 minutes, until it’s lightly browned. Remove from oven.

Layer 4 slices of Swiss cheese over the prebaked crust. Add the thinly sliced corned beef in an even layer. Spoon the sauerkraut mixture over the meat. Top with the remaining 4 slices of Swiss.

Roll out the second half of dough, pinching closed any perforations. Roll to roughly a 9-inch square. Place it over the filling. Press the edges of the top and bottom crusts to seal.

Brush the top crust with the beaten egg white for a light sheen. Use a small knife to make a couple of tiny vents in the top so steam can escape.

Bake for 15–20 minutes, until the top is golden and the cheese is melted. Let the bake cool for 5 minutes before slicing into squares.