Heat milk and butter in a small saucepan or microwave on high until butter melts and mixture is just warmed to 120°F to 130°F, 30 to 45 seconds.
Pour into bowl of stand mixer fitted with paddle attachment.
Add sugar, egg, yeast, and salt and 1 cup of flour, stir to mix. Add the mashed potato and mix.
Next, add the rest of the flour and the ground cinnamon and with a wooden spoon (or your mixer) stir until it all comes together.
Turn onto a lightly floured surface and knead by hand for about 8-10 minutes or until it becomes soft and elastic.
If dough is very sticky, add more flour by tablespoonfuls but do not add more than2 tablespoons ( use your mixer to knead the dough if you like)
Form dough into a ball.
Grease the bowl that you used for mixing with oil and transfer dough to bowl, turning to coat.
Let dough rise in warm draft-free area until doubled in volume in about 1-2 hours.
Gently punch down dough to release air.
Transfer to floured work surface.
Roll out to about 15×18-inch rectangle.
Brush dough with softened or melted butter leaving ½-inch border.
Combine cinnamon, sugar and pecans in a bowl and sprinkle evenly on the dough.
Starting at the long side, roll dough into log, pinching gently to keep it rolled up.
With seam side down, cut dough crosswise with thin sharp knife (or a dental floss or thread) into 18 equal slices (each about ½ to ¾ inch wide).
Grease two 9x13 inch glass baking dishes with butter or spray with non-stick spray.
Divide rolls between baking dishes, arranging cut side up (there will be almost no space between rolls).
Cover and let rise until double in volume (30-45 minutes)
Position rack in center of oven and preheat to 375°F.
Bake rolls until tops are golden, about 20 minutes.
Remove from oven and invert immediately onto rack.
Cool 10 minutes.
Turn rolls right side up.