Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper to prevent the cookies from sticking and to ensure even baking.

In a large mixing bowl, cream together the softened unsalted butter, creamy peanut butter, granulated sugar, and packed brown sugar until smooth and fluffy. I find that starting the mixer on low speed and working up helps incorporate everything evenly.

Add the large egg and vanilla extract to the creamed mixture, then mix until everything is well combined and smooth.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt until evenly mixed.

Gradually add the dry ingredients from Step 4 into the wet mixture from Step 3, mixing until just combined. Make sure not to overmix, as this can make the cookies tough.

Shape the dough into 1-inch balls. Flatten each ball, place a mini Reese's Cup in the center, and wrap the dough around the candy to form a ball. I like to chill the dough for about 10 minutes before shaping if it feels too sticky, as it makes wrapping the candies easier.

Arrange the stuffed cookie balls on the prepared baking sheet about 2 inches apart to allow for spreading. Bake in the preheated oven for 8-10 minutes, or until the edges are lightly golden. Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.