1. For thicker brownies use a 9 inch by 9 inch pan and start checking at 22 minutes; For extra fudgy texture underbake slightly and cool fully before cutting; Swap semisweet chips for dark chocolate chunks or add 1/2 cup chopped peanuts; Use natural peanut butter only if well stirred and thick otherwise the swirl can spread too much; Store airtight up to 4 days or freeze sliced up to 2 months