Cream butter/margarine, sugar, and vanilla. 

Add eggs; beat well. 

Combine flour and baking soda; add alternately with chocolate syrup to creamed mixture. 

Stir in peanut butter chips/chocolate chips. 

Pour batter into greased 13x9x2-inch pan (I use a 9x9x2 pan, and it works just fine).

Bake at 350 degrees for 30-35 minutes (depending on how soft or cake like you want your brownies, use a toothpick to tell).

Cool; frost with Peanut Butter Brownie Frosting.  Makes 24 brownies (give or take).

PB Brownie Frosting

Combine 1/3  cup sugar, 1/4 cup evaporated milk and 2 Tbsp butter in a small saucepan. 

Stir over medium heat until mixture come to full boil; remove from heat. 

Quickly stir in 1 cup Reese's Peanut Butter Chips until melted (I use regular ol' creamy peanut butter, it works just as well.); and 1 tsp. vanilla. 

Beat to spreading consistency; frost brownies. Cut into 24 brownies.

I personally use chocolate chips instead of PB chips in the brownies and I use regular Creamy Peanut Butter instead of PB chips in the frosting.  It works just as well I think, plus you get a kind of Reese cup taste to it.  (*See Picture)