Add the black sesame seeds to a high speed blender and grind to a fine powder.

In a medium size saucepan, melt chocolate and butter over medium heat. Remove from heat and let cool slightly.

To the bowl of a food processor, add ground black sesame seeds, flour, cocoa powder, salt, and baking soda. Pulse to combine. Add slightly cooled chocolate/butter mixture, sugar, egg, and vanilla. Mix until a dough forms.

Wrap the dough in cling wrap and refrigerate for 30 minutes.

Preheat oven to 375 degrees F. Line 2 baking sheets with parchment paper.

Working with 1/3 of the chilled dough at a time (keep remaining dough in refrigerator until ready to use), roll out between two pieces of parchment paper. Use a round cookie cutter (about 2 inches in diameter) to cut out circles. Place cut out cookies on prepared baking sheets and bake 9-11 minutes. Let cool on baking sheet for 5 minutes before transferring cookies to a wire rack to cool completely. Repeat with remaining dough.

To make the filling, add all of the ingredients to a food processor. Blend until smooth. Transfer filling to a piping bag fitted with a large circle icing tip. Pipe filling onto the flat side of half of the cookies. Top with flat side of remaining cookies.