Preheat oven to 425°F. Lightly butter 2 cookie sheets. Combine flour, baking powder and salt in bowl. Add shortening and cut in until mixture resembles coarse meal. Stir in cheese. Add buttermilk and onions and mix well. Turn out dough onto lightly floured surface and roll out to thickness of 1/2 inch. Cut out biscuits using 1 1/2-inch round biscuit butter. Gather scraps and reroll. Cut out additional biscuits. Transfer biscuits to prepared cookie sheets. Bake until puffed and light golden, about 15 minutes. Cool on rack. (Can be prepared 8 hours ahead. Cover and let stand at room temperature.) Preheat oven to 350°F. Split and lightly butter biscuits. Stuff with ham. Place on cookie sheets. Bake biscuits just until heated through, about 5 minutes.