Preheat the oven to 375 degrees Fahrenheit. Grease a mini muffin tin, and set aside.
In a large bowl, sift together the flour, baking soda, and salt. Set aside.
1 ¾ cups all-purpose flour, 1/2 teaspoon baking soda, ½ teaspoon kosher salt
In a second bowl, cream the butter, peanut butter, granulated sugar, and brown sugar together. Add the egg, milk, vanilla, and cream again.
8 Tablespoons unsalted butter, 3/4 cup smooth peanut butter, ½ cup granulated sugar, ½ cup light brown sugar, 1 large egg, 1 teaspoon vanilla extract, 1 Tablespoon milk
Gently stir the flour mixture into the bowl of wet ingredients.
Use a cookie scoop to roll the dough into 1-inch balls, and place them in the muffin tin.
Bake 8 minutes or until the cookies are light brown and puffed.
Remove from the oven, and immediately press a peanut butter cup into the center of each cookie, stopping roughly ⅔ of the way down.
40 mini peanut butter cups
Cool slightly in the pan before transferring to a wire rack to cool completely.
Store in an airtight container at room temperature for up to 4 days.