In a mixing bowl, combine 2 cups all-purpose flour, whole wheat flour, sugar, yeast, basil and celery salt; set aside.
Place potatoes and water in a saucepan; cook until tender. Drain, reserving 1 cup cooking liquid; cool liquid to 120 degrees F-130°. Meanwhile, mash or rice potatoes; measure 1 cup (refrigerate remaining potato for another ruse). Combine potato liquid, butter, eggs and mashed potato; add to dry ingredients. Beat until smooth. Add enough of the remaining flour to form a soft dough. Turn onto a floured surface; knead until smooth and elastic, about 8-10 minutes. Place in a grease bowl; turn once to grease top. Cover and refrigerate overnight or up to 3 days, punching down daily.
To bake, punch dough down. Pinch off small portions of dough; roll into 1-in. balls. Place three balls each in greased muffin cups. Cover and let rise until doubled, about 1-1/2 to 2 hours. beat egg yolk and water; brush over rolls. Bake at 375 degrees F for 20 minutes or until golden brown. Remove from pans and cool on wire racks.