Make the levain: mix together 50g ripe sourdough starter, 100g rye flour, and 100g water. Cover lightly and place on the counter to ferment for 12 hours.

After 12 hours, check your levain for readiness. It should be bubbly throughout and have risen, and have a mild sour smell. If these signs are not present, check again in 30 minutes. There will probably only be a handful of bubbles on the surface, but the bottom and sides should be very bubbly.

Place your mashed potatoes in a large mixing bowl. Use a fork to make sure they are mashed very smooth. Add the rye flour, salt and caraway seeds and mix thoroughly with a fork.

Add the water, molasses and the entire ripe levain to the bowl and mix thoroughly with a spatula. You should have a runny, smooth mixture.

Lastly, add the all-purpose flour and mix until well combined. You will have a somewhat sticky dough, but it should cling together and should no longer be runny.

Lightly cover and leave on the counter in a warm place for bulk fermentation.

Set a timer for 30 minutes, and when it goes off perform a set of stretch and folds. Repeat twice more at 30 minute intervals.

Leave the dough to sit for the remainder of bulk fermentation: 2 hours and 30 minutes more, for a total of 4 hours.

At the end of bulk fermentation, assess for readiness: the dough should be visibly risen and puffy, with bubbles present. If it has not risen, leave and check again in 30 minutes.

Lightly grease a baking sheet or a 10 inch cake pan ( my preference) and set aside.

Turn the dough out onto a clean work surface. Use your hands and a bowl scraper to shape the dough into a round. Place it, pinched side down, on your prepared pan. This is sticky dough and you might find it helpful to very lightly oil your hands, or wet them.

Lightly cover your dough and leave it on your counter in a warm place to proof for 2.5-3 hours, until quite puffy and risen.

Toward the end of your proofing time, preheat the oven to 425 degrees Farenheit.

Bake at 425 degrees for 15 minutes, then lower the oven temperature to 375 and bake for 15 more minutes.

When done, the dough should be browned, and sound hollow when tapped. It will feel pretty dense.

Toward the end of the baking time, whisk together water and sugar. When you remove the loaf from the oven, brush the glaze over the top of the loaf, before removing it to a cooling rack.

Allow to cool completely before slicing.

This keeps in a tightly sealed bag at room temp for about 2-3 days, or it freezes well!