Step 1

Preheat oven to 350°F. Line baking sheets with parchment paper or silicone liners.

Step 2

Whisk together the flour, baking soda, and salt. Set aside.

Step 3

Using an electric mixer on medium speed, beat the butter, peanut butter, and brown sugar until light and fluffy. Add the egg and vanilla, and mix well.

Step 4

Reduce mixer speed to low. Gradually add the flour mixture, mixing just until combined.

Step 5

Drop dough by tablespoonfuls onto prepared baking sheets, leaving about 2 inches between cookies. Use a fork to make a crosshatch design on top of each cookie.

Step 6

Bake, one pan at a time, 12 to 16 minutes, or until lightly browned. Cool on pans for 5 minutes. Then transfer the cookies to a wire rack to cool completely.

Step 7

Using an electric mixture on medium speed, beat the butter and sugar until thoroughly combined. Add the vanilla and marshmallow creme, and beat until smooth.

Step 8

Spread the frosting on the bottom of half of the cookies. (I use about 2 to 3 teaspoons of frosting.) Top each frosted cookie with an unfrosted cookie so that the bottoms face each other.