CRUST: Place all ingredients in food processor and pulse until combined. Press mixture firmly into parchment-paper lined 9 x 9-inch (23 cm) baking pan and bake in preheated 350°F/180°C oven for 12 minutes. Remove from oven. Reduce heat to 325°F/165°C.
TOPPING: Puree sweet potatoes, melted butter, eggs and vanilla together in a blender until smooth. Combine remaining topping ingredients together in a large bowl. Stir in sweet potato mixture until smooth.
ASSEMBLE & BAKE: Spread filling evenly over crust. Bake until centre is set, about 25 minutes. Cool completely in pan on wire rack.
GARNISH & SERVE: Refrigerate until cold. Cut into squares. Place icing sugar in small fine-mesh strainer and tap side lightly to dust tops of bars with icing sugar.