Grease a shallow 11" x 7" baking pan with butter; line bottom with parchment or waxed paper. Place honey, butter and chocolate together in a large bowl placed over a pan of gently simmering water. Stir until butter melts; remove from heat. Stir all but 1/4 cup of muesli into honey mixture. Spread in prepared pan, smoothing top with the back of a spoon. Sprinkle remaining muesli evenly on top, pressing gently into surface of mixture. Refrigerate 1 to 2 hours or until set. Carefully remove muesli mixture from pan; remove paper. Cut into 8 squares. Cut each square in half to make 2 triangles. Arrange neatly on a serving dish or store in an airtight container in a cool place for 2 to 3 days.