In a food processor, pulse your dates and almond butter together until a nice paste forms. If your dates aren't soft, soak them in hot water for 10 min first.
Add the cacao powder and, if using, the melted cacao butter. Pulse again until you have a very thick and slightly sticky dough.
Transfer to a container, either a bread tin or just any tupperware, add the chopped nuts and combine. Press the mixture into your mold and refrigerate until ready to eat.
Notes
Use less almond butter if yours is very runny. Any nut or seed butter works :)