Add egg and butter in a large mixing bowl and mix until combined.
Sift the cake mix powder.
Add this sifted cake mix into the bowl of wet ingredients.
Mix until just combined. Don’t over mix.
Cover and chill dough for 1-2 hours so that it's not sticky and easier to handle. Do not skip this step!
Remove dough from fridge and divide in half. Work with one portion at a time and keep the other portion chilled in the fridge.
Roll dough between two sheets of wax paper or parchment paper and use a heart cutter to cut out pieces. Make sure you are leaving enough space between each cookie so that there is enough space for them to expand during baking.
Remove excess dough from around the shapes.
Bake at 350 degrees for 6-8 minutes or until the edges are firm.
Allow the cookies to cool completely and then, remove them from the tray.
Drizzle the tops with royal icing or melted white chocolate. Toss some sanding sugar on top, if you like. Enjoy!