In large bowl, combine brown sugar and 1/2 cup margarine; beat until light and fluffy. Add vanilla, maple flavor, 1 whole egg and 1 egg yolk; beat well.
Lightly spoon flour into measuring cup; level off. Stir in flour, baking soda and salt; mix well. Cover with plastic wrap; refrigerate about 1 hour for easier handling.
Heat oven to 350°F. Grease cookie sheets. Arrange pecan pieces in groups of 5 on greased cookie sheets to resemble head and legs of turtle. In small bowl, beat egg white. Shape dough into 1-inch balls. Dip bottoms in beaten egg white; press lightly onto pecans. (Tips of pecans should show).
Bake at 350°F. for 10 to 12 minutes or until edges are light golden brown. Immediately remove from cookie sheets. Cool 15 minutes or until completely cooled.
In small saucepan, combine chocolate chips, milk and 1 tablespoon margarine; cook over low heat, stirring constantly until melted and smooth. Remove from heat; stir in powdered sugar. If necessary, add additional powdered sugar for desired spreading consistency. Frost cooled cookies. Let frosting set before storing. Store in tightly covered container.