1) Preheat the oven to 450° F.
2) Grease a baking sheet and set aside.
3) In a bowl, sift together flour, baking powder, soda and salt.
4) Using two knives cut in shortening, in the flour mixture.
5) Stir in the sour milk.
6) Dust the working table with flour.
7) Place the flour mixture on the working table and knead until stiff dough forms.
8) Roll the dough into 1/2 inch thick.
9) Using biscuit cutter, cut the rolled dough.
10) Arrange on the prepared baking sheet and brush with butter.
11) Bake in the oven for 10 to 15 minutes or until golden brown.
12) Remove the baking sheet and allow the biscuits to cool completely.
13) Serve as desired with hot tea or coffee.