Preheat your oven to 350 degrees Fahrenheit. Then, line your jellyroll pan with parchment paper. Doing so covers the inside bottom of your pan. After that, spray your parchment paper with a non-stick cooking spray. Afterward, set it aside.
Then, prepare your cake mix. And be sure to follow the box instructions. Afterward, spread your cake batter into your pan evenly. After that, bake for about 19 to 22 minutes. Likewise, you can bake till your cake cooks thoroughly.
One recipe of your favorite cake mix
When your cake finishes baking, remove your cake from the oven. After that, allow your cake to cool for about 10 minutes. Then, make sure to remove it from the pan to cool completely. In addition to that, remove the parchment paper.
You can prepare the icing while your cake is cooling. Then, combine all your icing ingredients in a medium-sized glass bowl. Afterward, heat it over a double boiler until the icing becomes smooth and warm. Also, remove from heat.
2 pounds of powdered sugar, 1/2 cup of light corn syrup, 1 1/2 tsp of vanilla extract
After that, cut your cake in half using a large serrated knife. Likewise, you can use a cake slicer. Then, remove the top half of your cake. Also, fill the bottom layer with your desired jam or frosting. Because of that, make sure to utilize an offset spatula. Also, put the top half back.
1 to 1/2 cups of jam frosting or any filling of your choice
Afterward, cut your cake into one-inch squares using a sharp knife. Then, arrange your cake slices into your cooling wire rack. After that, place the rack into a rimmed pan.
Then, pour your icing over the cake slices to coat the tops and sides. Also, if the icing starts to dry, transfer each slice from the rack. Afterward, transfer into a plate.
Finally, decorate your cake slices with icing. Then, you can drizzle ganache over the top of your petit fours if you desire.