Grate cheese and mix with softened butter, margarine, salt and pepper until light. Add flour and mix thoroughly (you may need to get your hands into the mixture to incorporate all the flour).
Form the mixture into 3 or 4 rolls, about the diameter of a quarter. Wrap each in aluminum foil and chill overnight.
The next day, cut into thin slices and press a pecan half on top of each, if you wish. Bake on ungreased cookie sheet at 350 to 375 F for about 15 minutes or until the edges are lightly browned. Can be made 3 to 4 days ahead and stored in airtight container.
Note: If desired, add 1 cup of finely chopped pecans to dough. Small portions of the dough can be rolled into marble-sized balls, put on ungreased cookie sheets, flattened with a fork and baked at 350 F until lightly brown around the edges.