Line the bottom and sides of a 9x5x3-inch loaf pan with waxed paper.
Cream butter and sugar. Beat in egg and corn syrup.
Whisk together flour, ½ teaspoon ginger, salt and baking soda.
Stir flour mixture into creamed butter mixture until well blended.
Divide dough in half. To one half add ¾ teaspoon ginger, cinnamon and molasses and blend well. To the other half blend in lemon juice and lemon peel.
Spread ginger mixture evenly in prepared pan. Spread the lemon mixture evenly over the ginger mixture. Cover and place in the freezer until firm.
Preheat oven to 375°F. Turn dough out of pan and remove waxed paper.
Cut dough in thirds length-wise; cut each third crosswise into ¼-inch slices. Place slices ¾-inch apart on ungreased cookie sheet.
Bake 8 to 10 minutes or until lightly browned at edges. Transfer cookies to wire racks; let cool. Store in airtight container.
Dough can be prepared days or weeks in advance and kept frozen before slicing and baking.