In a mixing bow, cream butter and sugar. Add eggs and vanilla; mix well.Combine flour, coca, and cream of tartar;gradually add to creamed mixture. Stir innuts. Spread half into a greased 13in x 9in x2in. baking pan. Combine coconut,condeensed milk and vanilla; carefully spread over chocolate layer. Top with the remaining chocolate mixture.
Bake at 350.F for 40-45 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack.For frosting, combine sugar,milk, and butter in a suacepan; cook and stir until sugar is dissolved. Add the remaining ingredients. Cook and stir until marshmallows and chips are melted. Cool until mixtures reaches spreading consistency, about 25 min. Spread over cooled brownies.Cut into bars.. I usually crush up some walnuts for the top. Yield 4 dozen.