Preheat your oven to 180°C (350°F) and line a baking sheet with parchment paper.
In a large bowl, cream the butter and vegetable oil together until light and fluffy.
Add the egg and vanilla sugar, mixing well.
In a separate bowl, combine the flour, cornstarch, baking powder, and powdered sugar. Gradually add the dry ingredients to the wet ingredients, stirring until just combined.
Gently fold in the chocolate chips until evenly distributed.
Drop spoonfuls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 12-15 minutes or until golden around the edges. Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
