Preheat your oven to 350°F (175°C).
Line a 9x13 inch baking pan with parchment paper.
In a large mixing bowl, combine the melted butter, packed brown sugar, granulated sugar, egg, and vanilla extract. Whisk until smooth and creamy.
Add the baking soda, salt, and flour to the wet mixture. Mix until just combined.
Gently fold in the chocolate chips.
In a separate bowl, combine the sweetened condensed milk, ground cinnamon, and a pinch of salt.
Spread half of the cookie dough evenly into the prepared pan. Layer the peanut butter cups on top, followed by the sweetened condensed milk mixture.
Dollop the remaining cookie dough over the filling.
Bake for 25-30 minutes, or until the edges are golden.
Allow to cool for 15 minutes, then lift out using the parchment paper and cool completely before cutting.