Bring 1 C. of water to boil in a medium large saucepan or in a larger glass bowl in the microwave. Remove from heat.
Add in this order:
2 C. sugar and stir a minute or so
½ C. butter
½ C. Peanut Butter
¼ C. vegetable oil
½ C. plain yogurt or buttermilk
1 tsp. vanilla
¼ tsp. salt or none
¼ C. cornstarch (or 2 T more flour)
Blend well with a wire whisk
1 tsp. soda
2 Cups flour
Mix well and pour into a 10x15 inch pan. Sprinkle with 1 C. chocolate chips (if desired) and bake for 20-25 minutes until the top is solid.
Frost with peanut butter frosting.
¼ c. butter
1/3 C. peanut butter
3 C. powdered sugar and enough milk to make a creamy frosting.