In a large mixing bowl, beat butter and the 1/3 cup shortening with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, sour cream, egg, vanilla, lemon peel, baking powder, mace, baking soda, and salt. Beat until combined. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour with a wooden spoon. Divide dough in half. Cover and chill for 1 to 2 hours or until easy to handle.
Bake in a 375 degree F oven for 7 to 8 minutes or until edges are firm and bottoms are very lightly browned. Transfer to wire racks to cool.
For icing, combine the 2 cups powdered sugar and 2 tablespoons milk in a small mixing bowl. Stir in additional milk, 1 teaspoon at a time, until of drizzling consistency. Tint icing as desired with liquid or paste food coloring. Frost cooled cookies with white or tinted icing. Let dry.
Creamy White frosting:
For Creamy White Frosting, beat 1/2 cup shortening with an electric mixer on medium speed for 30 seconds. Slowly add 1 cup sifted powdered sugar, beating well. Beat in 1 tablespoon milk. Gradually beat in 1-1/4 cups sifted powdered sugar and 1 teaspoon milk. Add additional milk, 1 teaspoon at a time, until frosting is of spreading consistency. Tint as desired with liquid or paste food coloring.
Divide Creamy White Frosting into three or four portions. Leave one white and tint the others the same pale colors used for the icing. Use a small writing tip (#1 or #2) in a decorating bag to decorate iced cookies with a pattern of dots and lines to simulate French knots and stitches (see photo). Let stand on wire racks until set. Store cookies in layers separated by waxed paper in a shallow, covered container. Makes about 48 cookies.