Preheat oven to 375 degrees.  Using about 1/4 cup of the butter, generously grease the bottom and sides of the cast iron skillet. 

Cut up the apple slices and place on top of the greased cast iron skillet.

In a mixing bowl, sift the flour, sugar, cinnamon an salt together.  Cut up the 1/2 cup of remaining butter using two knives into the flour mixture.  The flour mixture will stick to the butter to create a topping for the apples.   Sprinkle evening over the apples.

Put in the oven for 40-45 minutes or until the top is golden brown.  Cool before serving.