In a heavy 2-qt. saucepan, combine sugar, milk, 1/2 cup butter, vanilla and egg yolks; blend well. Cook over medium heat for 10 to 13 minutes or until thickened and bubbly, stirring frequently. Stir in coconut and pecans. Remove from heat and cool to room temperature.
Reserve 1 1/4 cups of topping mixture; set aside. In a large bowl, combine the cookie ingredients and remaining topping mixture. Stir by hand until thoroughly moistened.
Heat oven to 350 degrees. Shape dough into 1" balls. Place 2" apart on ungreased cookie sheets. With thumb, make an indentation in center of each ball. Fill each indentation with rounded 1/2 teaspoon of the reserved 1 1/4 cups of topping.
Bake 10 to 13 minutes or until set. Cool 5 minutes and remove from pans. Cool completely. Makes appx. 5 dozen.