MELT butter on medium low heat in large saucepan; remove from heat. Add sweet potatoes; mash with a fork or spoon. Add evaporated milk.
RESERVE 2 tablespoons pineapple for garnish. Stir remaining pineapple, brown sugar and cinnamon into sweet potato mixture. Cook on low heat, stirring occasionally, for about 10 minutes or until part of liquid evaporates. Serve warm.
GARNISH with reserved pineapple and mint leaves, if desired.