Dice the sweet potatoes into 2-inch chunks.
Bring a large pot of salted water to a boil. Place the sweet potato chunks in the boiling water and let them boil about 15 minutes, or until they are tender. Drain the sweet potatoes using a colander and let them set a few minutes to allow the water to evaporate entirely.
Blend potatoes, butter, and syrup using an electric hand mixer on low speed. Add the half and half or milk a little at a time until the potatoes reach the desired consistency.
Season to taste with salt and pepper. Top with cinnamon if desired and serve warm.