Toast the sesame seeds in a dry skillet over medium heat, stirring constantly, about 3-5 minutes. Black seeds will not turn golden, so go by smell and a faint popping sound. Pull them as soon as they are fragrant.
Let the toasted seeds cool completely.
Process the seeds in a food processor for 2-3 minutes, in short bursts of 1/4 to 1/2 minute, scraping down the sides as needed.
Once the seeds are broken down, add 1 tablespoon of cocoa powder and the powdered sugar. Add more cocoa if you want a stronger chocolate flavor.
Add 2 tablespoons of oil and process until smooth. Add more oil a little at a time if needed, since the cocoa absorbs some.
Store in an airtight container in the refrigerator, up to about one month.