In a large mixing bowl, cream together the butter and sugar until light and fluffy, about 3-4 minutes. Stir in vanilla extract and a pinch of salt.

In a separate bowl, whisk together flour, cocoa powder, and chocolate chips until combined. Gradually add to the butter mixture, mixing until no dry spots remain.

Pour heavy cream into another bowl and whisk until stiff peaks form. Chill if too runny for a stable consistency.

Scoop out cookie dough, flatten it in hand, place creamy filling in center, and mold dough around it to form a ball. Roll in mixed nuts.

Preheat oven to 350°F (175°C). Place cookie balls on a lined baking sheet and bake for 12-15 minutes until edges are set. Centers should remain soft.

Cool on a wire rack for about 10 minutes. Dust with powdered sugar if desired before serving.