Peel and cut potatoes into chunks, boil until tender, mash until smooth, spread on baking sheet to cool completely.
Stir yeast into warm milk, let stand 10 minutes until foamy.
Mix cooled mashed potatoes and eggs in stand mixer with paddle attachment until smooth.
Add yeast mixture to potato mixture.
Combine flour, salt, and sugar in separate bowl.
Switch to dough hook, add dry ingredients, mix on low 15 minutes until dough pulls away from bowl.
Add softened butter gradually while mixing on medium, knead 10 minutes until smooth and elastic.
Place dough in oiled bowl, cover, let rise 1-1.5 hours until doubled.
Divide dough in half, shape into rounds, rest 10 minutes.
Shape into logs, place in greased 9x5 loaf pans.
Cover, let rise 30-45 minutes until 1 inch above pan rim.
Bake at 375F for 30-35 minutes until golden brown and internal temp reaches 185-190F.
Remove from pans immediately, cool on wire rack.