Preheat the oven to 350°F (175°C).
Line a 12-cup muffin tin with paper liners or lightly grease the cups.
In a large bowl, combine the creamy peanut butter, granulated sugar, and light brown sugar. Mix until smooth and creamy.
Add the egg and vanilla extract to the peanut butter mixture. Stir until fully incorporated.
In a separate small bowl, whisk together the baking soda, salt, and all-purpose flour.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined to form a soft dough.
Divide the dough evenly into the 12 muffin cups, pressing the dough down slightly to form a cup shape with an indentation in the center.
Bake the cookie cups for 8 minutes.
Remove the muffin tin from the oven and immediately press one mini Reese’s peanut butter cup into the center of each cookie cup, gently pressing down so it is slightly embedded.
Return the muffin tin to the oven and bake for an additional 4 minutes, or until the cookie edges are golden and the cookie cups are set.
Remove from the oven and allow the cookie cups to cool in the pan for 10 minutes.
Transfer the cookie cups to a wire rack to cool completely before serving.