Preheat oven to 350 degrees F.
In the bowl of a standing mixer, or large mixing bowl with a hand mixer, beat the shortening and milk for 3 minutes.
While still mixing, add the vanilla sugar.
In a separate bowl, whisk together the flour, baking powder and salt.
Add the flour mixture to the shortening/milk mixture in three batches. Make sure to scrape the sides and bottom of the bowl very well.
Separate the yolks from the whites of 4 eggs. Add the egg whites to the batter and beat until mixed. Don't overmix.
Spray a 10-inch cast iron skillet with Baker's Joy OR coat well with shortening and dust with flour.
Pour batter into prepared skillet.
Bake for 35 to 40 minutes. Cake is done when a knife inserted in center comes out clean.
Cool completely on a wire rack. Lightly dust with powdered sugar if desired.
If not using vanilla sugar, add 2 teaspoons pure vanilla extract or vanilla paste with the regular sugar.