Sift together 1 1/2 cups flour, baking soda and salt. Cream 1/2 cup butter and gradually add 1/2 cup brown sugar, creaming well. Add egg and egg yolk and beat well. Blend in vanilla and maple flavoring. Add the dry ingredients gradually, mixing thoroughly. Chill to slightly firm dough.
Preheat oven to 350 degrees F (180 degrees C).
Arrange pecan halves in groups of five on greased baking sheets to resemble head and legs of a turtle. Shape dough into balls; dip bottom into unbeaten egg white and press lightly onto nuts. Use a rounded teaspoon of dough for each, so tips of nuts will show when cookies are baked. Bake for 10 to 13 minutes. Do not overbake. Cool; frost tops generously with Chocolate Frosting.
To Make Frosting: Combine 2 (1-ounce) squares of unsweetened chocolate ( or 1/3 cup semi-sweet chocolate pieces), 1/4 cup milk and 1 Tablespoon butter in top of double boiler. Heat over boiling water until chocolate melts; blend until smooth. Remove from heat; add 1 cup sifted confectioners' sugar. Beat until smooth and glossy. If too thin, add more confectioners' sugar until the desired consistency.