Preheat the oven to 180°C (160°C fan forced). Lightly grease 2 x 12-hole non-stick muffin pans and line the base of each with a small circle of baking paper.
Melt the butter in a small pan. Remove from the heat and stir in the brown sugar. Drop a teaspoonful of the butter and sugar mixture into each muffin hole. Cut each pineapple slice into 8 small pieces. Arrange 5 pieces of pineapple in each muffin hole. (There will be a few pieces left over that can be added to a few of the holes as extras.)
Open the cake box, remove enclosed frosting sachet and reserve for another use. Place the cake mix, eggs, melted butter and milk in a bowl, then whisk (by hand or using an electric mixer) for 2-3 minutes until smooth and creamy. Divide the mixture evenly among muffin holes.
Bake for 18-22 minutes until the cakes are risen and golden and a skewer inserted into 1 cake comes out clean. Remove from the oven and leave in the pan for 2-3 minutes, then run a small palette knife around each cake to loosen. Place a baking sheet over each muffin tray and invert each tray and sheet to release the cakes. Allow to cool until warm or completely cool.
To serve, pipe a swirl, or spoon a dollop of whipped cream on top of each warm or cold cake and top with a cherry. Store any leftover cupcakes in an airtight container in the fridge for 1-2 days.