Coat a 9-inch cake pan with cooking spray and set aside (or use large ramekins for individual servings. In a small saucepan over medium heatheat brown sugar and 1 stick of butter. Whisking occasionally until sugar is dissolved. Bring to a boil and cook until the caramel thickens and turns to a deep brown, approximately 3 minutes. Remove from heat and whisk in rum and 1 teaspoon salt. Pour caramel into prepared cake pan/s and swirl around to coat bottom of pan. Set aside and let cool completely, at least 30 minutes.
Preheat oven to 350 degrees
Meanwhilein a medium bowl whisk together flour, baking powder, cinnamon and remaining salt.
Inthe bowl of an electric mixer combine sugar and butter until light and fluffy. Add vanilla; beat in eggsone at a time. Reduce mixer speed to low and incorporate 1/2 of the dry mixture and 1/4 cup milk. Repeat with the remaining dry ingredients and the milk. Arrange pineapple rings in cake pan/s atop caramel. fill in spaces between rings with pineapple chunks. Carefully pour batter over pineapple then smoth cake using rubber spatula. Bake the cake/s until toothpick inserted in the center comes out clean. Approximately 30 to 50 minutes. Transfer to a wire rack and allow to cool for 30 minutes. Run a sharp knife round the sides of the cake pan/s to loosen the cake then invert onto large serving platter.