Preheat oven to 350 degrees. Spray 20 regular-size muffin tins with non-stick cooking spray (I like Baker's Joy for baking like this).
Combine cake mix, pudding mix, sour cream, vegetable oil, eggs, and reserved pineapple juice in a large bowl. Use an electric mixer (or you can beat quickly by hand) for about 2 minutes or until it's completely mixed together.
In another bowl, mix together melted butter and brown sugar.
Cut each pineapple slice into four pieces.
To assemble cupcakes, spoon a heaping teaspoon of the brown sugar mixture into the bottom of the tin. Place a cherry in the center (rounded side down) and then place 2 pineapple slices on top. Measure out 1/4 cup of cake batter and pour on top of pineapple slices.
Bake for 20 minutes or until toothpick placed in the center of the cupcakes comes out clean. Let cupcakes cool for 5 minutes, then run a knife around the edges of the cupcakes to loosen them and remove from cupcake pan.
Serve warm.
Notes
You can also use a homemade cake mix for this recipe.