Preheat oven to 425 degrees F (220 degrees C). Grease a well-seasoned cast iron skillet with the shortening, and place it in the oven as it heats.
Whisk together the flour and milk in a bowl, to make a thick but still runny batter.
Remove the hot greased skillet from the preheated oven, and quickly sprinkle a pinch of garlic salt over the bottom of the skillet. Immediately pour in the batter, and sprinkle the top with a pinch of garlic salt.
Return the skillet to the oven, and bake in the preheated oven until the cake has risen and the top is golden brown, about 20 minutes.