MIX flour, brown sugar, corn starch, salt, baking powder and baking soda in a large bowl. Cut in butter using a pastry blender OR two knives. Add egg yolks and vanilla. Mixture will be crumbly. Press into an ungreased 13 x 9-inch pan.
BAKE in a preheated 350ºF oven for 12 to 15 minutes. Remove from oven and sprinkle with marshmallows; return to oven for 3 to 5 minutes, until marshmallows are puffy.
HEAT corn syrup, butter and peanut butter chips in a saucepan over low heat until smooth. Remove from heat. Add vanilla, cereal and peanuts.
SPREAD over baked crust; chill 1 hour or until firm.