Preheat your grill to medium heat.
In a cake pan, spread the melted butter and sprinkle the brown sugar evenly over the bottom.
Arrange the pineapple rings on top of the brown sugar mixture, and place a cherry in the center of each ring.
In a mixing bowl, combine the flour, granulated sugar, baking powder, and salt.
Add the milk, beaten eggs, and vanilla extract to the dry ingredients, and mix until smooth.
Pour the batter over the pineapple rings in the cake pan.
Place the cake pan on the grill, close the lid, and cook for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the grill and let it cool for 10 minutes. Invert the cake onto a serving plate and serve warm.