In the bowl of a stand mixer fitted with a paddle attachment, add sourdough starter and 545 grams cold water. Mix until just combined.

Add flours, sugar, molasses, caraway, malt powder, instant yeast, and salt. Mix on low speed until well incorporated and a shaggy dough forms.

Increase speed to medium and mix for 20 minutes.

Transfer dough to a floured work surface. Knead a small amount of dough to ensure the dough passes the windowpane test.

Wrap dough tightly in plastic wrap and let sit for 15 minutes at room temperature.

Divide dough into 5-ounce portions. Using both hands, roll each portion into a large rope.

Wrap dough rope around your finger, squeezing tight to roll the ring around your wrist.

Place on a cornmeal-dusted cutting board and let sit for 1½ hours at room temperature.

Once proofed, place in refrigerator, uncovered, for 24 hours.

The next day, heat oven to 450°F. Bring a pot of water to a boil.

Place cornmeal in a shallow baking dish and set aside.

Working in batches, add dough rounds to the water. Cook for 45 seconds. Flip and cook an additional 45 seconds.

Dredge bottom sides of boiled dough in cornmeal. Transfer to a sheet tray.

Bake for 9 minutes. Flip and bake an additional 9 minutes, or until both sides are lightly browned. Set aside.

On a sizzle tray, place desired amount of corned beef. Top with cheese. Bake until cheese has melted. Let cool.

Slice Bagel in half. Smear dressing on both Bagel halves.

Using a spatula, transfer cheesy corned beef to the bottom half. Close sandwich and serve with a side of sauerkraut.