Preheat oven to 350°.
Combine 1/4 cup coconut milk and cornstarch in a small saucepan; stir with a whisk until cornstarch is completely dissolved. Add remaining 3/4 cup coconut milk, stirring until smooth. Bring to a boil over medium heat, and cook 1 minute, stirring frequently. Remove from heat, and cool completely. Add 1/4 cup powdered sugar and vanilla, stirring with whisk.
Place 1 phyllo sheet on a large cutting board or work surface (cover remaining dough to keep it from drying); lightly coat with cooking spray. Cut sheet into 4 squares, and layer squares in a muffin cup, 1 square at a time, pressing down in the center after each addition so dough takes the shape of the cup. Ruffle edges to create the appearance of a nest. Repeat with remaining phyllo sheets to make 8 nests. Bake at 350° for 5 minutes or until golden. Remove from oven, and cool completely.
Combine mango and pineapple in a medium bowl. Spoon 2 tablespoons coconut milk mixture into each phyllo nest; top each with 1/4 cup fruit mixture. Dust evenly with remaining 2 teaspoons powdered sugar.