Combine butter, brown sugar, white sugar, vanilla, and egg until well combined. Stir in the flour and the baking soda (dough will be stiff). Pat dough onto an ungreased 12 inch pizza pan or on a cookie sheet.
Bake at 350 degrees F (175 degrees C) for 15 minutes or until golden brown. Remove cookie from oven and let it cool.
In a saucepan heat the chocolate chips, remaining butter or margarine, and milk over very low heat. Stir until chocolate is melted. Remove the chocolate mixture from the heat and stir in the confectioners' sugar. Beat until smooth, glossy, and of spreading consistency. If frosting is not glossy, stir in a few drops of hot water. Spread over the top of the baked and cooled cookie.
Immediately sprinkle with pecan halves, M&M candies, and coconut. Press lightly into frosting. Drizzle top with the melted white chocolate. Let stand until set. Remove from pan if desired. Cut into wedges.