Preheat the oven to 180°C (160°C fan forced). Grease and line 2 x 20cm square cake pans with baking paper.
Open the cake box, remove enclosed frosting sachet and reserve for another use. Make bake and cool the cake mix as directed on the box, adding the eggs, butter and milk.
Trim the rounded tops off the cakes (if necessary) and brush off any crumbs. Place 1 cake, cut-side up, on a cake board. Spread with a quarter of the vanilla frosting. Top with the second cake and spread the sides and top of the cake with half of the remaining vanilla frosting. Chill for 30 minutes, then spread the remaining frosting onto the top and sides of the cake leaving a smooth surface. Chill for a further 30 minutes.
On a surface lightly dusted with icing sugar, roll out the blue icing to a large 2-3mm thick rectangle. Cut 2 x 2.5cm wide strips from the longest length and place onto the cake, crossing in the middle, for the ribbon. Trim the edges neatly at the base of the cake.
Cut 2 x 24cm long x 2.5cm wide strips from the icing. Using one strip, fold in each end from the outside to the middle to make a bow. Press in the middle to seal and tuck a little paper towel or a wooden spoon handle into the loop to keep the shape. Cut a 6cm x 2.5cm piece of icing and wrap around the middle of the bow. Press gently to seal. Cut the second 24cm length of icing in half and cut an inverted V into one end of each. Place onto the cake with the straight end pressed onto the middle of the cake, where the 2 other ribbons cross over and a slight kink at the end to make it look like a ribbon.
Place the bow on top and press gently to stick. Set the chocolate beans into the vanilla frosting around the cake to decorate. Remove the paper towel or wooden spoons from the bow once ready to serve.