How to make it

1. Preheat the oven to 350°F (177°C) and line two baking sheets with parchment paper.
2. In a bowl, whisk together the flour, cocoa powder, baking soda, and salt.
3. In a separate bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy.
4. Beat in the egg and vanilla extract until well combined.
5. Stir in the melted chocolate until the mixture is smooth.
6. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
7. Scoop tablespoon-sized balls of dough (about 30 g each) onto the prepared baking sheets, spacing them 2 inches apart.
8. Bake for 10-12 minutes, until the edges are set but the centers are still soft.
9. Let the cookies cool on the baking sheets for 5 minutes, then transfer to a cooling rack to cool completely.
10. To make the filling, beat together the peanut butter and butter until smooth and creamy.
11. Gradually add the powdered sugar, vanilla extract, and salt, beating until smooth.
12. Once the cookies are cool, spread about 1 tablespoon of peanut butter filling onto the flat side of half the cookies.
13. Top with the remaining cookies, pressing gently to create sandwiches.