Preheat oven to 350°F (175°C). Grease a 9x13-inch baking pan or line with parchment paper.
In a large bowl, cream together the peanut butter, softened butter, granulated sugar, and brown sugar until smooth.
Beat in the eggs one at a time, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients and mix until just combined.
Stir in the chocolate chips, if using.
Press the dough evenly into the prepared baking pan.
Bake for 12–15 minutes, or until the edges are lightly golden and the center is set.
Allow to cool completely in the pan before cutting into 16 squares.
Notes
Store in an airtight container at room temperature for up to 5 days.