Place the peeled potato chunks and 4 c water in a medium saucepan. Bring to a boil. Add 1 tsp salt and cook, partially covered, for 20 to 25 minutes, or until the potatoes are very tender.

Drain the potatoes, reserving the cooking water. Mash the potatoes thoroughly until smooth.

Measure 3 c of the reserved potato cooking water. If needed, add additional water to reach 3 c.

Place the mashed potatoes and 3 c potato water in a large mixing bowl. Stir well and allow the mixture to cool to 70°F to 80°F.

In a 1-cup measuring cup, stir the active dry yeast into 1 c of the cooled potato water mixture. Add the yeast mixture back into the bowl with the mashed potatoes and remaining potato water. Let stand for 5 minutes.

Add 2 c unbleached all-purpose flour to the potato mixture. Stir until combined. Let the mixture rest for 3 to 4 minutes.

Add the remaining 1 tbsp salt and the softened butter. Mix until incorporated. Add the whole wheat flour and stir briefly.

Add 2 c unbleached all-purpose flour and stir until fully incorporated.

Turn the dough onto a generously floured surface. Knead for about 10 minutes, adding additional all-purpose flour as needed to prevent excessive sticking. The dough should remain soft and slightly moist.

Place the dough in a large clean bowl or rising container. Cover with plastic wrap or a lid. Let rise for about 2 hours, or until doubled in volume.

Turn the dough onto a well-floured surface. Knead gently for 3 to 4 minutes. The dough should remain moist and slightly sticky.

Divide the dough into 2 unequal portions: one larger portion, about two-thirds of the dough, and one smaller portion, about one-third of the dough. Cover the smaller portion loosely with a kitchen towel.

Butter a 9 x 5 x 2.5-inch loaf pan.

Flatten the larger dough portion into an approximate 12 x 8-inch oval. Roll the dough from a narrow end to form a loaf. Pinch the seam closed.

Place the dough seam side down in the buttered loaf pan. The dough should reach about three-quarters of the way up the sides of the pan.

Cover the loaf pan with plastic wrap. Let rise for 35 to 45 minutes, or until puffy and almost doubled in volume.

Butter a 13 x 9-inch sheet cake pan or shallow cake pan.

Cut the smaller dough portion into 12 equal pieces. Shape each piece into a ball using a floured hand.

Place the dough balls in the prepared pan, leaving about 1/2 inch of space between each roll.

Cover the rolls with plastic wrap. Let rise for about 35 minutes, or until puffy and almost doubled.

Preheat the oven to 450°F.

Dust the risen loaf and rolls lightly with all-purpose flour, or brush the tops lightly with melted butter.

Using a very sharp knife, slash the loaf crosswise two or three times.

Place the loaf and rolls in the oven. Bake at 450°F for 10 to 15 minutes.

Reduce the oven temperature to 375°F and continue baking.

Bake the rolls until golden brown, about 30 minutes total.

Bake the large loaf for about 50 minutes total, or until golden brown and hollow-sounding when tapped on the bottom.

Transfer the rolls to a wire rack to cool.

Remove the loaf from the pan and place it back on a baking sheet. Bake for an additional 5 to 10 minutes, if needed, until the corners feel firm when gently pinched and the bottom sounds hollow when tapped.

Transfer the loaf to a wire rack. Allow the loaf and rolls to cool for at least 30 minutes before slicing. Rolls may be served warm or at room temperature.