Heat oven to 350°F. Lightly grease a 24-cup mini muffin pan.
Stir the melted topping butter with the brown sugar until sandy. Spoon a heaping 1 teaspoon into each cup.
Place a cherry half in each cup. Add a small spoonful of pineapple tidbits over the sugar.
Whisk flour, granulated sugar, baking powder, and salt in a bowl.
In another bowl, whisk pineapple juice, milk, vanilla, melted batter butter, and the beaten egg until smooth.
Fold wet ingredients into dry just until combined; do not overmix.
Divide batter among cups, about 1 tablespoon per well, covering the fruit.
Bake 13–16 minutes until tops spring back and edges look caramelized.
Cool 3–4 minutes. Run a thin knife around edges, then invert the pan onto parchment and lift off.
Serve warm or at room temperature. Wipe the pan and repeat if baking in batches.