Cinnamon-Crunch Sweet Potato Muffins

Sweet potatoes are available year-round but are most abundant in markets in autumn and winter. Some of these edible roots-members of the morning glory family-have tan skin and light yellow flesh; others have darker red-orange skin and flesh. The latter type is often called a yam in the United States, although it is not a true yam. Red-orange sweet potatoes are slightly moister and sweeter than the tan variety, which has the same texture as a russet potato when cooked and mashed.