Preheat the oven to 350℉.
Cut butter into small squares and place on the bottom of the 11x7 baking dish or mini angelfood cake pans.
Place the baking dish into the oven to melt the butter.
In a small bowl, stir to combine the brown sugar with water.
Once the butter is melted, remove the baking dish from the oven and pour the brown sugar slurry onto the butter.
Place the raspberries randomly on top of the brown sugar.
Place the pineapple rings on top of the entire baking dish or one ring in each mini bundt cake slot.
In a large mixing bowl, stir the softened butter and sugar.
Add the eggs, vanilla, and milk and stir to combine.
Fold in the flour and baking powder just enough to mix the batter.
Pour the batter on to the pineapple rings and carefully spread the batter with a spatula, being careful not to move any of the pineapple rings below.
Bake the cake in the preheated oven for 30 minutes or until a toothpick inserted into the middle of the cake comes out clean.
Remove the baking dish from the oven and allow to cool for 5 minutes.
Place a serving platter on top of the baking dish and invert to transfer the cake to a plate.
Allow to cool for 10 minutes before serving. This cake is excellent served warm, but can be stored in an airtight container for up to 4 days.