Preheat oven to 325°. Grease and lightly flour a 9″x 13″ baking pan.
Whisk together flour, baking soda, and salt. Set aside.
Using an electric mixer on low speed, beat butter and brown sugar until fluffy (about 2-3 minutes). Add peanut butter and beat well. Mix in egg and vanilla.
Gradually add dry ingredients and mix well. Stir in 1/2 cup chocolate chips, 1/4 cup white chocolate chips, 1/4 cup peanut butter chips, and pecans.
Spread mixture evenly into prepared pan. Bake 25-30 minutes, or until lightly browned.
Remove from oven and sprinkle 1/4 cup chocolate chips and 1/4 cup peanut butter chips on top of bars. Allow to sit for 1-2 minutes. Using a spatula, smooth out chips as they begin to melt.
Cool for 20 minutes. Sprinkle with remaining 2 tablespoons each chocolate chips, white chocolate chips, and peanut butter chips. Cool completely before cutting into bars.