Heat ½ cup unsalted butter and ¾ cup brown sugar in a saucepan over medium heat, stirring constantly until butter melts and sugar dissolves.
Preheat the oven to 350°F. Lightly grease a 9×13 baking dish with nonstick cooking spray. Pour the melted caramel sauce into the pan and spread evenly using a spatula.
Arrange the pineapple slices into rows, starting with the middle row first then adding pineapple slices around it. Add one maraschino cherry into the center of each pineapple slice. You can also add more cherries in other open spaces between the pineapple if you’d like.
In a medium bowl, mix together the dry ingredients including 2 cups all purpose flour, 2 tsp baking powder and ¼ tsp salt.
In a separate large bowl, add the ½ cup unsalted butter, ½ cup granulated sugar and ¼ cup dark brown sugar. Use a hand mixer to mix the ingredients until creamy.
Add one large egg and mix together. Add the second large egg and combine until smooth and creamy.
Now add the dry ingredients to the wet ingredients bowl and mix until just combined. Next, add ½ cup milk and mix it all together.
Add ½ cup pineapple juice (saved from the canned pineapple) and 1 tsp vanilla extract and mix until just combined. This will create the cake batter.
Gently smooth the cake batter over top of the pineapple slices in the baking dish. Use a spatula to smooth it into an even layer. Place in the oven to bake for 30-35 minutes or until the edges are golden and a toothpick comes out clean when poked through the cake.
Let the cake cool for at least 1 hour in the baking dish. To invert, place a baking sheet or large cutting board over top of the pan. Using both hands holding the pan and dish together, flip them over so that the pineapple cake is now on the baking sheet. Slice around a piece of pineapple and serve.