Preheat the oven to 350 F and lightly grease a mini muffin tin with oil or butter to help prevent sticking.  

In a food processor fitted with an “S” blade, combine the dates and 1/4 of water, and process until the dates have broken down into a paste. 

Add in the tahini, cocoa powder, baking soda, cinnamon, vanilla, salt, and vinegar (and flax seeds, if using), and pulse and process until a sticky, uniform dough is created.  You may need to add 1 to 2 more tablespoons of water to help it blend smoothly.  The batter will be thick and sticky but shouldn't be completely solid. 

Use a tablespoon or 1-ounce cookie scoop to help you scoop the batter into the greased mini muffin tin. Sometimes it's thick enough I use my hands, but I like the final texture better with a wetter, stickier batter (even if it's harder to work with).

Wet your fingers and gently flatten each mound of dough.  Press in one or two chocolate chips per muffin on the top of the batter if desired.

Bake until the tops look dry and the centers are still soft to the touch, about 10-12 minutes.  I definitely like mine a tad underdone (though this does make them more prone to sticking in the pan, FYI).

Remove from the oven and let the brownies cool completely, at least 20 minutes, before attempting to remove them from the pan. They firm up as they cool, but are very fragile when warm.

Run a knife or offset spatula around the edge of each brownie to help loosen them to be removed, then finish cooling on a rack.  Serve immediately or store them in an airtight container for up to 1 week (they'll keep a bit longer in the fridge).