Preheat oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper.
In a medium bowl, mix together peanut butter, sugar, and egg until smooth. Add vanilla and salt if using.
Press mixture evenly into prepared pan. Sprinkle with chocolate chips if desired.
Bake for 15-20 minutes until edges are lightly golden. Center will look slightly soft.
Cool completely in pan (about 30 minutes) before cutting into bars.
Notes
For best results, use conventional creamy peanut butter (not natural/oily varieties)Bars will firm up as they coolStore in airtight container for up to 5 days