In a small bowl, cream together the butter and sugars. Beat in the egg and vanilla. Add in the flour, salt and baking soda. Mix until just combined. Fold in the potato chips.
Spray an 8x8 baking pan with cooking spray. Press the cookie dough into the bottom of the pan. Pour the bag of M&M's on top of the cookie dough. Press the M&M's slightly into the cookie dough. Sprinkle the macadamia nuts on top.
Bake at 350 degrees for 22-25 minutes, or until the cookie is lightly browned.
In a small bowl, melt the chocolate chips in the microwave. Do this slowly, as white chocolate can burn very quickly! Use a spoon to drizzle the chocolate over the bars. Cut into squares and serve!