In a small bowl, dissolve the yeast and 1 teaspoon sugar in the warm water until bubbly, about 5 minutes
Combine 2¾ cups flour, remaining sugar, salt and butter in a stand mixer. Add the dissolved yeast and beat, using the dough hook, to make a soft dough (scraping sides as needed). Add an additional ¼ cup flour if the dough is too wet. Knead with the dough hook for 4 minutes. Turn the dough out onto a floured mat.
Roll out the dough to a 10x14 inch rectangle. Spoon the dressing down the center of the dough. Top with corned beef, cheese, and sauerkraut. Make cuts along sides of the dough, from the filling to the outer edge, at 1 inch intervals. Tuck the ends in first, then alternating sides, fold strips across filling.
Carefully move the bread to a parchment lined baking sheet. Brush the dough with egg white and sprinkle with caraway seeds.
Loosely cover the bread with a clean dishtowel and allow to rise for 30 to 45 minutes.
Preheat the oven to 400°F.
Remove the dish towel, and bake 25 minutes, or until golden brown and cooked through, then slice and serve warm.
Notes
If you don't own a stand mixer, mix the dough by hand until all of the ingredients are well-incorporated, then turn the dough onto a floured surface and knead it well for 4 minutes or so.