Preheat oven to 350°F. Beat peanut butter, brown sugar, corn syrup, butter, eggs and vanilla in large bowl with mixer at medium speed until smooth.

Reduce speed; beat in flour, baking powder and salt until well blended.

Stir in 1-1/2 cups of chocolate chips.  Spread evenly in ungreased 15 X 10 X 1-inch baking pan.

Bake 25 minutes or until lightly browned.  Cool completely on wire rack. 

In small, heavy saucepan over low heat, stir remaining 1/2 cup chocolate chips until melted and smooth. 

Drizzle over surface; cool before cutting.