How to Make It
In a small bowl, whisk the flour with the baking powder and salt. In a large bowl, using a handheld electric mixer, beat the butter until smooth. Add the sugar and beat on medium speed until light and fluffy. Add the egg and vanilla and beat until smooth. Add the dry ingredients all at once and beat at low speed just until combined.
Divide the dough in thirds and place in 3 small bowls. Stir the cherries and red food coloring into the dough in one bowl. Fold the melted chocolate and walnuts into the dough in the second bowl. Roll each piece of dough into a 12-inch log and wrap in wax paper. Chill just until slightly firm, about 30 minutes.
Unwrap the dough logs and place them on a work surface. Press each log into a 12-by-2-inch block. Stack the blocks with the plain dough in the middle. Press on the blocks lightly to adhere, being careful to retain their rectangular shape. Cover and chill until very firm, at least 2 hours.
Preheat the oven to 350°. Transfer the dough to a work surface and gently tap it on all sides to straighten the sides and corners. Using a very sharp knife, cut the dough into scant 1/4-inch-thick slices and arrange them on 3 large cookie sheets. Bake one sheet at a time for about 17 minutes, until the cookies are very lightly browned. Using a spatula, immediately transfer the cookies to a wire rack to cool.
The cookies can be stored in an airtight container for up to 2 weeks.