Heat oven to 400°F Grease muffin pans. Stir together first 5 ingredients in large bowl. In small bowl whisk oil, egg and buttermilk together. Add liquids to dry ingredients and stir just to mix, do not beat. Stir in mangoes and nuts. Spoon into muffin tins using a small measuring cup or ladle, filling 3/4 full. Sprinkle a pinch of sugar over top of each muffin. Bake 25 minutes till brown. Immediately turn muffins out of pans to cool.