Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.

In a large mixing bowl, cream together the peanut butter, softened butter, granulated sugar, and brown sugar until light and fluffy. Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.

In a separate bowl, whisk together the flour, baking soda, and salt. Gradually stir the dry mixture into the wet mixture until a dough forms.

Scoop out tablespoon-sized portions of dough and roll them into balls. Place them on the baking sheets, spacing them about 2 inches apart. Flatten each slightly with a fork dipped in sugar, creating a crisscross pattern.

Bake for 10–12 minutes or until the edges are lightly golden. Let the cookies cool completely on a wire rack.

To prepare the marshmallow filling, melt the miniature marshmallows in a microwave-safe bowl in 20-second intervals, stirring between each, until smooth. Alternatively, use marshmallow fluff for ease. Let it cool slightly while remaining spreadable.

For the chocolate topping, combine the chocolate chips and heavy cream in a small saucepan over low heat. Stir constantly until the chocolate is fully melted and smooth. Remove from heat and allow it to cool slightly.

To assemble the sandwiches, pair the cooled cookies in matching sizes. Spread the marshmallow filling on the flat side of one cookie and sandwich it with another.

Dip or drizzle the top of the cookie sandwiches in the chocolate topping. Let the chocolate set on a wire rack at room temperature or in the refrigerator.