Place chicken in a greased 8″ x 8″ baking dish and season with salt and pepper.
Melt butter in a sauce pan and add brown sugar and onion. Cook for 4-5 minutes. Add rum, pineapple juice, diced pineapple, sweet chili sauce and soy sauce. Cook for 5 minutes.
Place cornstarch in a small bowl and stir in 1/4 cup of sauce from pan and blend well to dissolve cornstarch. Return the cornstarch mixture to the rest of the sauce in pan and cook until sauce has thickened.
Pour sauce over chicken in baking dish. At this point you can refrigerate the chicken covered for up to 24 hours. Bake at 350 for 1 hour, or until chicken has cooked through. Serve with rice
*you can substitute any rum or use rum extract. If you use rum extract, add another 1/3 cup pineapple juice to recipe.