Preheat oven to 350 degrees F (180 degrees C).
In a large mixing bowl, beat
Butter (1 cup)
Caster Sugar (1 cup)
Vanilla Extract (1 tsp)
medium speed of an electric mixer until well combined. Beat in Egg Yolk and
All-Purpose Flour (2 cups)
. Stir in
Walnuts (1 cup)
Spread into a 10-inch by 15-inch Pyrex by 2-inch baking dish that has been sprayed with
Nonstick Cooking Spray (as needed)
Now, beat the white of the
until frothy. Spread beaten egg white over mixture in baking dish. Sprinkle the remaining Walnuts (1/2 cup) [Chopped] over the top.
Bake for about 20 to 25 minutes, or until set and lightly browned. A toothpick inserted into the center should come out clean.
Immediately sprinkle with
Semi-Sweet Chocolate Chips (1/2 cup)
Peanut Butter Chips (1/2 cup)
. Let stand 5 minutes.
Spread melted chips to form marbled frosting. Cool completely and cut into bars. Enjoy!