Preheat the oven to 400°F. Generously grease the muffin tins (for 24 muffins), and set aside. In a medium bowl, combine the flour, baking powder, nutmeg, salt, and 1 teaspoon of the cinnamon, and mix well. In a large bowl, combine 1½- cups of the sugar, the sweet potatoes, and butter, and beat with an electric mixer until smooth. Add the eggs and mix well. Alternately add small amounts of the flour mixture and the milk to the sweet potato mixture, stirring just to blend after each addition. Do not overmix. Fold in the raisins and pecans. Spoon the mixture into the prepared muffin cups.
In a small bowl, combine the remaining 2 tablespoons sugar and ½ teaspoon cinnamon, and sprinkle the cinnamon-sugar over the muffins. Bake for 25 to 30 minutes, until lightly browned and a toothpick inserted into the center comes out clean. Allow the muffins to cool thoroughly, transfer them to an airtight container, and freeze for up to 3 months.
Remove the muffins from the freezer, and allow them to sit at room temperature for 2 hours.
To reheat the muffins in the microwave, put them in a single layer in a resealable plastic bag, but do not seal the bag. Microwave the muffins for 45 seconds to 1 minute, until thoroughly warmed.
To reheat the muffins in the oven, preheat the oven to 400°F. Wrap the thawed muffins in aluminum foil, and bake them for 15 minutes until thoroughly warmed.