Remove from oven, sprinkle with chocolate chips and return to oven briefly, about 1 minute. Remove from oven, spread melted chocolate chips with a knife and sprinkle on nuts. Cool and cut into bars.

Sprinkle the remaining 1/2 cup of toffee pieces, 1/4 cup of M&Ms, and 1/4 cup of chocolate chips over the top of the batter. Bake until a wooden pick inserted in the center comes out clean, 40 to ...