3 to 4 medium potatoes, scrubbed and very thinly sliced on mandoline
Kosher salt and black pepper
3 tablespoons cornstarch
3 to 4 tablespoons beef stock
Olive oil, for brushing plus 1 tablespoon
2 tablespoons butter
1 medium onion, very finely chopped
4 cloves garlic, finely chopped
1 teaspoon paprika
1/2 pound sauerkraut, drained and rinsed
1/2 to 3/4 pound corned beef, very finely chopped
2 cups shredded Gruyère cheese
1/2 cup sour cream
1/4 cup ketchup
2 tablespoons pickle relish
Preheat oven to 425°F.
Place potatoes in a large, shallow bowl or dish and season with salt and pepper; sprinkle with cornstarch.
Brush a large, 12-inch pizza pan liberally with olive oil. Arrange potatoes around pan working all the way to edges and overlapping the slices evenly to form the potato crust. Press crust down to set then sprinkle with a 3 to 4 tablespoons stock. Brush liberally with olive oil. Bake 15-20 minutes, or until potatoes are cooked through.
In a skillet over medium heat, melt butter. Add onions and garlic, and season with a little salt, pepper and the paprika. Cook to tender, 7-8 minutes. Add corned beef and stock, and cover. Cook until crispy on the bottom.
Top the potato crust with a thin layer of sauerkraut, then corned beef and cheese. Bake or broil in the lower third of the oven to bubbly and brown.
In a small mixing bowl, mix together the sour cream, ketchup and relish. Transfer to a squeeze bottle and squeeze onto top of pizza, or dollop evenly around the pizza.