To prepare crust, lightly spoon flour into a dry measuring cup, and level with a knife. Place the flour, granulated sugar, and 1/8 teaspoon salt in a food processor; pulse 2 times or until combined. Add 2 tablespoons butter and shortening, and pulse 4 times or until mixture resembles coarse meal. With processor on, add ice water through food chute, 1 tablespoon at a time, processing just until combined (do not form a ball). Shape mixture into a 6-inch log; wrap in plastic wrap coated with cooking spray. Freeze 30 minutes.
Shape the dough into 24 balls, and place 1 ball in each of 24 miniature muffin cups coated with cooking spray. Press dough into the bottoms and up the sides of the muffin cups.
Preheat oven to 425°.
To prepare the filling, place syrup and next 5 ingredients (syrup through egg) in a bowl; beat with a mixer at medium speed for 1 minute or until well blended. Add sweet potatoes and milk; beat until well blended. Spoon about 4 teaspoons filling into each muffin cup.
To prepare streusel, combine hazelnuts and 2 tablespoons brown sugar in a small bowl; cut in 1 1/2 teaspoons butter with a pastry blender or 2 knives until mixture resembles coarse meal. Sprinkle streusel evenly over tarts; bake at 425° for 10 minutes. Reduce heat to 350° (do not remove tarts from oven); bake for 12 minutes or until the filling is set. Cool for 5 minutes on a wire rack. Run a knife around outside edges. Remove tarts, and cool completely on wire rack.