Preheat oven to 350°F.
Grease or spray with non-stick cooking spray a 10-inch springform pan.
Drain pineapple, keeping liquid.
Mix together flour, sugar, and baking powder.
In a large mixing bowl, mix the egg, butter, brown sugar, milk, 3 tablespoons pineapple juice, and rum.
Stir in pineapple tidbits.
Stir in flour mixture until well mixed.
Pour into prepared springform pan.
Bake, about 30 to 35 minutes or until lightly browned.
Cool and sprinkle with coconut if desired.
