1Combine yeast and 1/2 cup warm water in a 4-cup liquid measuring cup, and let mixture stand 5 minutes. Stir in buttermilk.
2Combine flour and next 4 ingredients in a large bowl; cut in shortening with a pastry blender or fork until mixture resembles coarse meal. Add buttermilk mixture, stirring with a fork just until dry ingredients are moistened.
3Turn dough out onto a well-floured surface, and knead 4 to 5 times.
4Roll dough to 1/2-inch thickness; cut with a 2-inch round cutter, and place on lightly greased baking sheets. Cover and let rise in a warm place (85°), free from drafts, 1 hour.
5Bake at 425° for 10 to 12 minutes or until golden. Split each biscuit, and spread evenly with Mustard Butter. Stuff biscuits with ham.
6To prepare the mustard butter,
Stir together all ingredients until well blended.