Preheat the oven to 450 degrees F.

In a medium bowl, combine the flour, sugar, baking powder, baking soda and salt. Cut in the shortening with a fork until it looks like cornmeal. Add the milk, a little at a time, stirring constantly until well mixed.

Turn the dough out onto a lightly floured surface. Knead lightly two or three times. Roll out the dough with a floured rolling pin to 1/2-inch thickness. Cut with a 2-inch cutter.

Place the biscuits in a greased iron skillet. Gently press down top of biscuits. Brush the biscuits with half the melted butter. Bake for 14 minutes or until golden brown. Brush the hot biscuits with the remaining butter. Split the biscuits in half and ladle milk gravy over the hot biscuits.

Heat bacon grease in a cast iron skillet. Add the flour and whisk until smooth and bubbly about 1 minute. Add the warm milk slowly and bring to a boil. Reduce the heat to a low simmer and stir, until thickened, about 5 minutes, adding milk as necessary to control the thickness. Season the gravy with salt and pepper. Serve hot over biscuits.