Bring the milk and 1 ½ cups water to boil in a large saucepan on the stove.
Add the cubed potatoes.
Boil uncovered 13-15 minutes or until potatoes are fork tender.
Remove the pan from the heat but do NOT drain the potatoes.
After the potatoes have cooled to a warm temperature, measure out ½ cup of the liquid and ¼ cup of the liquid separately.
Drain the potatoes and discard the remaining liquid in the pan.
Add the ¼ cup of cooking liquid from the potatoes back into the pan and mash the potatoes with the liquid. Set the mashed potatoes aside.
Add the yeast to a large mixing bowl.
Pour the remaining 1/2 cup of warm cooking liquid from the potatoes into the bowl.
Wait 5-10 minutes, then add the prepared mashed potatoes, bread flour, sugar, salt, shortening and remaining 1 ½ cups water to the bowl.
Use an electric hand mixer or stand mixer with a dough hook attachment to mix the dough together for 3-4 minutes on high.
Place the dough on a lightly floured surface and knead for 10 minutes.
Pace the kneaded dough into a large oiled bowl and turn to oil each side.
Cover the bowl with a clean kitchen towel or plastic wrap and place in a warm area to rise.
Let rise for one hour. At this time the dough should have doubled in size.
Punch the dough down, then remove it from the bowl and separate into three equal loaves.
Place each loaf in a 5" x 8" loaf pan or shape into a loaf and place on a baking stone.
Cover again with a clean kitchen towel or plastic wrap for 30 minutes.
Preheat the oven to 375°F.
Remove cover and place bread in the oven to bake for 20 minutes, or until golden brown.
Flour: I've made this recipe with both bread flour and all-purpose flour. While I prefer the bread flour, either will work for this recipe.
Leftover mashed potatoes: If you want to make this recipe with leftover mashed potatoes, you'll need two cups of mashed potatoes to make the dough. Instead of using the cooking liquid from the potatoes to start the recipe with the yeast, simply substitute in 1/2 cup warm water.