Preheat the oven to 375F.
In a large mixing bowl, beat together the butter, vegetable oil, sugar, powdered sugar, and vanilla extract until smooth. Beat in the eggs one at a time until combined. Set aside.
In a large mixing bowl, whisk together the flour, baking powder, and cream of tartar. Add half of the flour mixture to the wet mixture and beat just until combined. Add the remaining flour and beat until all flour is combined, but do not over mix.
Scoop the batter into 1 to 1 ½ inch balls onto baking sheets lined with parchment paper. Tip: a cookie scoop is perfect for this task!
Sprinkle the top of each cookie with a pinch of granulated sugar.
Bake the cookies at 375F for 8-10 minutes, until they begin to lightly brown around the edges.
Remove the cookies from the baking sheet with a spatula and cool slightly on a wire cooling rack.