How to Make It
Preheat toaster oven to 325°F. Heat 4 tablespoons of the butter in a medium saucepan over medium-high. Whisk in brown sugar, and bring to a simmer. Add drained pineapple and salt; cook, stirring often, until thick and syrupy, 8 to 10 minutes.
Place 2 tablespoons of pineapple mixture in bottom of 4 lightly greased (8-ounce) ramekins. Press 1 cherry in center of each ramekin.
Beat together cake mix, egg, reserved pineapple juice, and remaining 2 tablespoons butter with an electric mixer on medium speed until combined, about 3 minutes. Pour 1/3 cup cake mix in each ramekin.
Bake in preheated oven until lightly golden and a toothpick inserted in the center comes out clean, 18 to 20 minutes. Let cakes stand 5 minutes before carefully inverting them onto a small plate.