Cook pineapple juice in a saucepan over medium-high heat 20 minutes or until reduced to 1/2 cup; set aside.
Sprinkle sugar in an 8-inch round cakepan; place over medium heat, and cook, shaking pan constantly, until sugar melts and turns a light golden brown. Remove from heat.
Process reduced pineapple juice, condensed milk, and next 4 ingredients in a blender until smooth, stopping to scrape down sides; stir in pineapple. Pour custard over caramelized sugar in pan. Cover with aluminum foil; place in a roasting pan. Add hot water to roasting pan to a depth of 1 inch.
Bake at 350° for 50 to 55 minutes or until a knife inserted in center comes out clean. Remove cakepan from water, and uncover; cool flan in cakepan on a wire rack 30 minutes. Cover and chill for 2 hours.
Run a knife around edge of flan to loosen; invert onto a serving plate. Garnish, if desired.