Cream the butter and sugar together until light and fluffy. Add the corn syrup, lemon rind and juice, rum, and spices and beat well. Gradually stir in the flour until the dough forms a ball. (The dough can be prepared in a food processor, using the same procedure.) If the flour has been packed closely in the measuring cup, you may find that the dough tends not to cohere into a ball. The addition of a teaspoon of two of water will correct the proportions. Divide the dough in two and pat each piece into a rectangular shape. Wrap and chill for 1 or 2 hours in the refrigerator or place in the freezer for 15 minutes. Preheat oven to 350. Measure out a large piece of aluminum foil that will fit a cookie sheet. Turn its shiny side down, place one of the rectangles of dough on it, and rap it a few times with a rolling pin to soften the chilled dough a little. Cover with a piece of wax paper the same length as the foil and fasten the two sheets together with several straight pins. Roll the dough between the foil and the wax paper as thin as you can. The thinner the better and crisper. Do not attempt to work too fast, but press down heavily on the rolling pin. The rolled-out dough should almost reach the edges of the wax paper. Lift the dough with with foil and wax paper onto the cookie sheet, foil side down. Remove the straight pins and carefully pull off the wax paper. Cut the dough into any shape you desire--squares, rectangles, diamonds, triangles--but leave in place after cutting. Make certain you cut through the dough; this will prevent excess breakage later. Place in the oven for about 10 minutes, or until the cookies are lightly browned. The ultrathin dough at the edges of the pan will brown faster than the rest. Repeat with the other half of the dough. Store in an airtight container. These crisps are not only extremely good, but very fragile as well. Avoid excessive handling. (Note: The second portion of dough can be frozen for future use.{ {23 calories per cookie} ----