Dip rim of glass into water and then coat with black sugar.
In a cocktail shaker, combine 3 ounces cold brew coffee, 1 ounce Kahlua, 2 ounces vodka, 1 ounce blk, and half an ounce of simple syrup. Shake to combine.
Strain into martini glass.
Serve immediately.
Notes
If you prefer your drinks to be less sweet, omit the simple syrup. The blk helps to dilute the drink a bit, the way ice would in a traditional black Russian. But you can omit this step if you want your drink stronger. You can also substitute regular water for the blk.