Beat sugar and butter until light and flufly. Add vanilla, maple flavoring, 1 whole egg and 1 egg yolk; beat. Stir in flour, soda and salt. Refrigerate for easier handling. Grease cookie sheet. Arrange pecan halves in groups of 5 to resemble head and legs of turtle. Beat 1 reserved egg white. Shape rounded teaspoon of dough into balls. Dip bottoms in whites and press into pecans. (Tips of pecans should show.) Bake at 350 degrees for 10-12 minutes or until brown around ed~ges. Remove and cool. In pan melt chips, milk, and butter on low heat until smooth. Stir in sugar. If necessary add more powdered sugar for consistency. Frost cookies.