Place the ground Wagyu beef in a bowl and mix in the salt and black pepper until just combined. Divide into 8 equal portions and shape each into a small patty about 2 inches wide.

Heat the olive oil in a large skillet over medium heat. Add the patties and cook for 3 minutes per side until browned and cooked through. Remove to a plate and cover loosely.

While the patties rest, mash the black garlic cloves into a paste with a fork. Stir the paste into the mayonnaise until smooth to make the aioli.

Spread the butter on the cut sides of the mini brioche buns. Toast the buns in the same skillet for 1 minute until lightly golden.

Spread a layer of black garlic aioli on the bottom half of each bun. Add a cooked patty, then finish with the top bun.