Preheat oven to 375. Add the butter, vegetable oil, sugar, and powdered sugar to a bowl. Mix for a couple minutes. Add egg and vanilla and mix until just combined.
Add flour, cornstarch, baking powder, salt, and mix until just combined. Divide the dough in half and add a couple drops of green food coloring to one half, and blue to the other. Mix until the color is evenly distributed.
Using a small cookie scoop or your hands, grab about 1 tbsp of each color of dough. Smoosh the colors together and form into a ball. Roll the ball in your hands to get a smooth finish.
Put up to 12 cookies on a baking sheet and bake at a 375 for 8 minutes. Let the cookies cool completely and enjoy!