Preheat the oven to 350°F/180°C. Line 2 cookie sheets with parchment paper or silicone baking mats. Set aside.

In a medium sized bowl, combine powdered sugar with corn starch and set aside.

In a separate bowl, combine butter with oil and eggs. Using a hand mixer, beat until well combined (30 seconds).

Add the cake mix, and mix until combined. The batter will be thick.

Add green food coloring, and mix again. I used Wilton green leaf gel coloring. Add enough to reach the desired shade.

Using a small cookie scoop, scoop dough balls directly into the powdered sugar and corn starch mixture. The dough balls will be very soft, gently roll in the mixture and transfer to the cookie sheets.

Bake, rotating the cookie sheets halfway through for 8-10 minutes or until the cookies have puffed up. If you cook for too long, the edges will brown and change color so try to avoid that.

Remove from the oven, allow to cool on the cookie sheet for 5 minutes then transfer to a wire rack and cool completely.

To decorate with hearts, use the leftover corn starch and powdered sugar, take 1 tablespoon and mix with 1 tablespoon of water. Use this as glue and attach the hearts. Or use icing.