1. Heat your oven to 350 degrees F (175 degrees C). Line a 12 cup muffin pan with cupcake liners. Lightly coat the liners with cooking spray. Alternatively, you can simply spray the pan cups well with cooking spray and skip the liners. Both methods work well and give nice results.
2. Get a large mixing bowl. Add the granulated sugar, brown sugar, oil, and egg to the bowl. Use a whisk to mix these ingredients together. Continue mixing until the mixture becomes dark and thick.
3. Now add the applesauce, sour cream, milk, and vanilla extract into the same bowl. Stir everything with the whisk until these wet ingredients are fully combined.
4. Add the all purpose flour, baking powder, ground cinnamon, and salt to the bowl. Switch to a wooden spoon or spatula for mixing. Stir the ingredients just until they are combined. Stop mixing as soon as no streaks of dry flour are visible. Do not overmix the batter.
5. Use a scoop to divide the batter among the prepared muffin cups. Fill each cup almost completely full. About three quarters full is good. A little bit more batter is also fine.
6. Place the pan in the preheated oven. Bake for 17 to 20 minutes. The tops of the muffins should look puffy and rounded when they are done.
7. Let the muffins cool in the pan for about 20 minutes. They should be cool enough to handle easily after this time.

For the Cinnamon and Sugar Topping

1. While the muffins cool slightly, prepare the topping. Pour the melted butter into one small bowl. In a separate bowl, stir together the granulated sugar and ground cinnamon for the dry topping mix.
2. Once a muffin is cool enough to hold, pick it up. Dip the top surface only into the melted butter. Immediately after dipping in butter, dip the buttery top into the cinnamon and sugar mixture. Gently roll the top part of the muffin around in the sugar mix. This helps the sides of the muffin top get coated as well.
3. Place the finished muffins on a cooling rack. Let them cool completely on the rack. You can also enjoy one warm right away. Store any leftover muffins at room temperature. Keep them in an airtight container to maintain freshness.