Bake cake and allow it to cool to room temperature.
Remove cake from pan and cover in saran wrap.
Chill in freezer overnight or 3-4 hours until it's firm.
Remove cake from freezer and discard saran wrap.
Use a sharp knife to cut out a shirt shape. You can draw a template on parchment paper and place that on top of the cake and use it as a guide, when making your cuts.
Use a spatula to cover the entire cake in icing smoothly. A few crumbs are fine.
Sprinkle your work surface generously with powdered sugar.
Roll out white fondant.
Spread it over your iced cake and trim excess along the bottom with a pizza cutter.
Add details on the sleeves. Roll out white fondant and cut two thin strips. Use the "stitch" cutter to create the stitch pattern. Stick these two strips on both the sleeves by brushing some water.
Use a rounded fondant tool (or even the non-pointed side of a wooden skewer) to create crease marks in the "armpit" area of the sleeve.
Make the collar. Roll out white fondant and cut out a thick strip. Use the "stitch" cutter to create the stitch pattern. Wrap this around the neck area of the cake by brushing some water. Hold the collar shape by stuffing it with crumpled gift wrapping tissue paper or crumpled aluminum foil.
Make the black belt. Roll out black fondant and cut out a thick strip. Use the "stitch" cutter to create the stitch pattern. Stick this along the waist of the shirt by brushing some water.
Roll out black fondant and cut out a thick strip again. Use the "stitch" cutter to create the stitch pattern. Fold it over to create a "knot." Stick this in the center of the belt by brushing some water.
Use a steamer (that you use for clothes) to steam the cake from about 1 feet away. This will dissolve all the powdered sugar residue that's on your cake and also add a nice shiny finish to the cake. Enjoy!