In a large bowl, combine 2 cups flour, sugar, yeast and salt.
In a small saucepan, heat water and butter to 120°-130°.
Add to dry ingredients; beat until smooth.
Stir in mashed potatoes and enough remaining flour to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, 6-8 minutes.
Cover and let rest for 10 minutes.
Divide into 16 pieces.
Shape each into a ball.
Place in 2 greased 8- or 9-in. cast-iron skillets or round baking pans.
Cover and let rise in a warm place until doubled, about 30 minutes.
Preheat oven to 400°.
Sprinkle tops of rolls with additional flour.
Bake until golden brown, 18-22 minutes.
Remove from pans to wire racks.
