Preheat oven to 180°C /350°F(160°C for fan-forced oven). Line bottom and sides of 20cm square cake pan with foil and well-grease. Remove enclosed frosting sachet if using Frosted Chocolate brownie mix and reserve for another use. Make and bake brownie mix as directed on box using water, oil and eggs. Transfer to cooling rack to cool completely; about 1 hour. Freeze in pan for 30 minutes.
Remove brownies from tin using foil to lift and peel away. Use sharp knife to cut brownies into 4 rows by 4 rows, making 16 brownie squares (about 5cm x 5cm each).
Spoon vanilla frosting evenly between 3 separate small bowls. Stir in different colour of food colouring into each bowl to desired shade of colour. Decorate as desired.
To decorate Polar Bear Brownie: frost top of brownie square thickly with vanilla frosting. Using fork, pull through frosting to outside of brownie to create “fur”. Dollop a small mound of vanilla frosting in center of brownie, place 1 brown chocolate button on top for nose, 2 mini brown chocolate buttons for eyes, and 2 white chocolate drops for ears. Pipe a mouth using black writing frosting tube.
To decorate Gift Brownie: frost top of brownie square with green frosting. Sprinkle 100's and 1000's on top of frosted brownie. Pipe 2 lines of red writing frosting tube across top to intersect in middle. Place in center 5 red chocolate buttons tipped on sides in a circle for a bow.
To decorate Santa’s Hat Brownie: frost top of brownie square with green frosting. Sprinkle top edges of brownie with candy sprinkles. Place 3 red chocolate buttons in a triangle on top of frosted brownie. Place 3 marshmallow pieces for hat’s brim and one on top of triangle for pom-pom.
To decorate Christmas Tree Brownie: frost top of brownie square with red frosting. Sprinkle top edges of brownie with candy sprinkles. Place 6 green chocolate buttons in a triangle on top of frosted brownie. Place 1 yellow mini chocolate button on top of triangle for star. Place one piece of licorice at bottom of triangle for tree trunk.
Store covered at room temperature.