01 -
Heat the oven to 350°F. Line two baking sheets with parchment paper.
02 -
In a large bowl, stir together the cake mix, softened butter, oil, eggs, vanilla, and green gel food coloring until a thick, evenly green dough forms.
03 -
Cover the bowl and chill the dough for 15 minutes, just until it is easier to scoop and roll.
04 -
Stir the powdered sugar and cornstarch together in a small bowl. Scoop the dough into 1 1/2 tablespoon balls and roll each one generously in the sugar mixture.
05 -
Place the dough balls 2 inches apart on the prepared sheets. Bake for 8-10 minutes, until the tops are puffed and cracked and the centers look set. Do not let the edges brown.
06 -
Let the cookies rest on the baking sheet for 1 minute, then gently press one heart sprinkle into the center of each warm cookie. Transfer to a wire rack to cool completely.