Peel and cut potatoes into 1" pieces; place in an 8-quart saucepan, cover with water and bring to a boil over high heat. Reduce heat to medium; cook potatoes until tender, about 25 minutes. Drain potatoes and return to saucepan; add butter, syrup, cinnamon, and season with salt and pepper; mash with a potato masher and serve with additional butter, if desired.