Beat 2 cups sugar, butter, and vegetable oil with an electric mixer in a large bowl until smooth.
Add egg yolks one at a time, allowing each egg to blend into the butter mixture before adding the next. Sift flour, baking soda, cream of tartar, and salt into the egg yolk mixture; stir. Stir in vanilla extract.
Roll the dough into walnut-sized balls.
Spread 1/4 cup sugar onto a flat surface.
Roll the balls of dough in sugar to coat. Arrange onto baking sheets spaced at least 2 inches apart.
Bake in preheated oven cooked in the middle, but not yet browned, about 15 minutes.
