Preheat oven to 350 degrees Fahrenheit. Grease nine x 13-inch pan.

Combine sugars, oil, vanilla, eggs, and 2/3 cup peanut butter until smooth.

Add dry ingredients until well combined.

Spread mixture into greased nine x 13-inch pan. Bake for 20 to 25 minutes. Remove from oven; do not shut off oven.

While the cake is still warm, scatter chocolate chips evenly over the pan and return it to the oven one minute longer, allowing the chocolate to melt.

Remove from oven and quickly drop remaining peanut butter over pan in 1/2 teaspoonfuls. Swirl and spread chocolate and peanut butter to marbleize and coat bars.

Cut while warm. Cool completely before serving.