Make the cookies: In a large bowl, cream together the sugar and butter until smooth. Beat in 4 whole eggs and 6 egg yolks, one at a time, mixing well after each. Mix in vanilla extract. Combine flour, baking powder, and salt; stir into the sugar mixture. Cover dough and chill for at least 1 hour.

Preheat the oven to 375 degrees F (190 degrees C). Grease cookie sheets.

On a floured surface, roll the dough out to 1/2 inch thickness and cut into desired shapes using cookie cutters. Place 2 inches apart on the prepared baking sheets.

Bake for 8 to 10 minutes in the preheated oven. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack.

While cookies are baking, make the frosting: Mix together the confectioners’ sugar, oil and 1 teaspoon vanilla until smooth. Gradually add enough hot water to achieve a spreadable consistency.

Spread frosting over warm cookies.