In advance: Make fondant bow (see below). Tint approximately 20 oz. of white fondant pink and knead with 2 teaspoons of Gum-Tex for added strength. Reserve remaining pink fondant mixture to make streamers and flat ribbon.
Prepare 2-layer 3 in. high cake for rolled fondant by lightly icing with buttercream. Tint approximately 36 oz. of fondant yellow. Cover cake; smooth with Fondant Smoother. To make flat ribbon, using reserved fondant mixture, cut a 1 1/2 x 16 in. strip; position on cake. Trim off excess, then remove. Position flat ribbon and bow pieces on cake. Roll 1/8 to 1/4 in. diameter white fondant balls and attach to cake with damp brush.
Roll out fondant 1/8 in. thick. Cut two 2 x 9 in. strips for loops. Cut a 1 1/2 x 4 in. strip for knot. Pleat each end of bow loop strips. Fold strips over to form a loop. Brush ends lightly with water, align ends. Position cotton balls inside loops to keep shape.
Shape the knot by pleating each end of fondant strip and wrapping it around middle of the pleated ends of bow loops. Remove cotton balls from loops.
For streamers, cut 1 1/2 in. wide strips, 5 and 6 in. long; cut V-shapes at one end and pinch together other end to fit under loops. To dry streamers, place pan flat, back side up, and position streamers, placing cotton balls beneath to shape. Let dry, then remove.