In a large bowl, cream together the peanut butter, softened butter, granulated sugar, and brown sugar until smooth and creamy.
Beat in the egg and vanilla extract until fully combined.
In a separate bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until a soft dough forms.
Press the dough evenly into a greased 8x8-inch baking dish.
In a microwave-safe bowl, combine the chocolate chips and heavy cream. Microwave in 30-second intervals, stirring between each, until smooth and fully melted.
Pour the chocolate ganache over the peanut butter base and spread evenly.
Refrigerate for at least 2 hours, or until the chocolate is set.
Cut into 16 squares and serve chilled.
Notes
Store in an airtight container in the refrigerator for up to 1 week.