Preheat the oven to 400° F. Spray a 12-cup muffin pan with nonstick cooking spray or use paper liners.
In a large bowl mix together the flour, sugar, baking powder, salt and cinnamon.
In a separate bowl, mix together the egg, eggnog and melted butter.
Stir the wet mixture into the dry mixture until just moistened (use as few strokes as possible, some lumps are okay.)
Divide the batter evenly between the 12 muffin cups.
Use a teaspoon to add a few dollops of cranberry sauce into each muffin.
Pull the spoon or a clean knife through each cup once or twice to swirl the sauce into the batter. If desired, sprinkle sparkling decorating sugar over the tops.
Bake for 15-18 minutes until the muffins are starting to brown and a tester inserted into the muffin comes out clean. Serve while warm.
Once cool store in an airtight container for 1-2 days.
As mentioned above, it's important to only use a few strokes to bring the muffin batter together. A few streaks of flour are okay. Over-mixing this batter will lead to muffins that are dense and tough.
You can use whatever cranberry sauce you have on hand: homemade or store-bought, with or without whole berries.