Peel yams and cut into 1/4-inch slices; drop into a bowl of water to keep from discoloring. Drain water and transfer to a large pot fitted with a steamer basket. Steam for 10 to 15 minutes or until tender when pierced with a fork. Preheat oven to 350 degrees and lightly butter a 13 x 9-inch baking dish. Stir together the brown sugar and cinnamon. Place half the yams, mangos, brown sugar mixture and butter in the dish. Repeat layers. (Dish may be covered and refrigerated for up to 24 hours at this point.) Bake at 350°F for 20 minutes; sprinkle with almonds and cook for 20 minutes more.