In food processor, pulse butter, flour, sugar and salt until mixture begins to form small lumps. Transfer mixture into a 13 x 9 in. pan; press evenly onto the bottom. Bake 15-17 minutes or until just golden. While crust is baking, prepare topping.
In large bowl, whisk together egg whites and sugar until combined well. Stir in flour and coconut.
Sprinkle chopped chocolate evenly over the hot crust. Allow it to melt; spread evenly with spatula. Drop small spoonfuls of coconut mixture onto chocolate; spread gently.
Bake 25-30 minutes or until top is golden. Cool completely in pan. Cut into 24 bars. Store cookies up to 5 days, covered, at room temperature.