In a microwave-safe bowl, melt ½ cup of unsalted butter in 20-second increments, stirring between each interval until fully melted. Allow to cool.

Whisk in ¾ cup of light brown sugar until smooth. Then add in one egg and 1 teaspoon of vanilla extract until well combined.

In a separate bowl, mix together 1¼ cups of all-purpose flour, ⅓ cup cocoa powder, ½ teaspoon baking soda, and ¼ teaspoon salt.

Gradually add the dry ingredients to the wet mixture, stirring until no flour streaks remain. Chill the dough for at least 1 hour.

Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.

Scoop about 3 tablespoons of dough, flatten slightly and prepare peanut butter filling.

Mix together ½ cup peanut butter, ¾ cup powdered sugar, and ½ teaspoon vanilla extract until smooth.

Place about 1 tablespoon of filling in the center of each flattened dough ball and encase it.

Optionally, add chocolate chips on top of each filled cookie.

Bake for 8 minutes, until edges are set but centers are soft. Cool before serving.