Step 1: Preheat your oven to 350°F (175°C) to prepare for the perfect bake.
Step 2: Line your 9x9 inch baking pan with parchment paper, leaving some overhang for easy removal later.
Step 3: In a medium saucepan over low heat, melt the butter. Once fully melted, remove it from the heat and let it cool slightly.
Step 4: Add the brown sugar and granulated sugar to the melted butter. Stir until well combined and smooth.
Step 5: Whisk in the egg and vanilla extract until the mixture is smooth and glossy.
Step 6: In a separate bowl, whisk together the flour, sea salt, and baking soda. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Step 7: Gently fold in the chocolate chips until evenly distributed throughout the batter.
Step 8: Chop the peanut butter cups into smaller pieces and fold them into the brownie batter, ensuring they are evenly dispersed.
Step 9: Pour the brownie batter into the prepared baking pan and spread it evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Step 10: Allow the brownies to cool in the pan for about 10 minutes, then lift them out using the parchment paper. Let them cool completely on a wire rack before slicing into squares.