Blend butter, ½ cup brown sugar, granulated sugar, egg yolks, and vanilla. Beat until well blended and smooth. Stir in flour, baking powder, soda, and salt. Spread dough in a greased 13x9-inch pan, spreading it to make an even layer. Sprinkle the top of the dough with chocolate chips, coconut, and nuts. Beat egg whites until foamy. Beat in 1 cup brown sugar, a tablespoon at a time, and continue beating until stiff and glossy, about 3 minutes. Spread meringue on top of dough, distributing it gently but evenly. Bake at 350 degrees F for 35 to 40 minutes. Cool and cut into bars.