In a large bowl, combine ½ cup (1 stick) butter (room temperature), ½ cup chunky peanut butter, ½ cup packed light brown sugar, and ½ cup granulated white sugar. Beat on medium speed with a mixer until the mixture is light and fluffy.
Add 1 large egg and 1 teaspoon vanilla extract; mix until thoroughly combined.
In a separate bowl, whisk together 1¼ cups all-purpose flour, ½ teaspoon baking soda, and ¼ teaspoon salt. Add the dry ingredients to the peanut-butter mixture and mix just until combined.
Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 2 hours.
Preheat the oven to 350°F. Line one or two baking sheets with parchment paper or silicone baking mats.
Unwrap the Snickers Miniatures. Set aside several Minis and chop them into small pieces to use as topping (aim for about 2–3 small pieces per cookie).
Scoop or measure dough into 1-inch balls (about 1 rounded tablespoon each). Flatten each ball in your hand, place one whole Snickers Mini in the center, then wrap the dough completely around the candy and pinch the seam to seal. Roll gently to form a smooth ball and place seam-side down on the prepared baking sheet. Leave enough space so cookies can spread—place only 6 to 8 cookies per sheet.
Use a fork to press a light criss-cross pattern on the top of each cookie. Press 2–3 of the chopped Snickers pieces onto the top of each cookie.
Bake the cookies 10 to 12 minutes, or until the cookies are set and no longer glossy on top. Remove the baking sheet from the oven and let the cookies cool on the sheet for about 5 minutes, then transfer them to a wire rack to cool completely.