Cook and Prepare the Potatoes

Place the diced potatoes in a medium saucepan and cover with water. Bring the water to a boil and cook until the potatoes are tender. Drain the potatoes, reserving one cup of the cooking liquid. Mash the potatoes until smooth and allow them to cool for 20–30 minutes.

Activate the Yeast

In the bowl of a stand mixer, combine the warm milk, sugar, and yeast. Whisk lightly until blended, then let the mixture rest for approximately five minutes, or until it becomes foamy.

Incorporate Dry Ingredients

Attach the dough hook to the mixer. Add the all-purpose flour, bread flour, and salt to the yeast mixture. Mix on medium-low speed until a rough, dry dough begins to form.

Add Wet Ingredients

Gradually pour in the reserved potato water while kneading, allowing the dough to come together. Follow with the mashed potatoes and softened butter, continuing to knead until the dough becomes cohesive and pliable.

Knead and Rest the Dough

Knead the dough on medium speed for about 10 minutes until it becomes smooth and elastic. Shape it into a ball and place it in a greased bowl. Cover with a kitchen towel or plastic wrap and let it rise in a warm area for about an hour, or until doubled in size.

Shape the Loaves

After the first rise, punch down the dough and transfer it to a floured surface. Divide it into two equal portions. Fold the sides of each portion inward and pinch to seal. Shape into smooth logs and place them in greased loaf pans. Cover lightly and let rise for another hour.

Bake the Bread

Preheat the oven to 350°F during the final rise. Once the dough has risen, bake the loaves on the middle rack for 35–40 minutes, or until the tops are golden and the bread is fully cooked through.

Cool and Slice

Remove the loaves from the oven and transfer them to a wire cooling rack. Allow the bread to cool completely before slicing or storing.