1Line 8x4-inch loaf pan with plastic wrap, leaving 1 inch of plastic wrap overhanging at 2 opposite sides of pan. In large bowl, beat butter and sugar with electric mixer on medium speed until light and fluffy. Beat in egg and peppermint extract. On medium-low speed, beat in flour and salt until blended.
2Divide dough in half. Tint half of dough with red food color, kneading with gloved hands until well blended. Press half of plain dough evenly in bottom of pan. Gently press half of red dough evenly over plain dough. Repeat layers with remaining dough. Cover with the plastic wrap; refrigerate 2 hours or until firm.
3Heat oven to 350°F. Remove dough from loaf pan; unwrap. Cut dough in half lengthwise. Cut each half crosswise into 1/4-inch slices. On ungreased cookie sheets, place slices 2 inches apart. Bake 10 to 12 minutes or until set. Cool 2 minutes; remove from cookie sheets to cooling racks.