For two caviar with egg cream on crispy brioche, first peel the boiled eggs and finely mash them together with the sour cream and apple cider vinegar. Season to taste with salt and pepper.
Cut out brioche slices with a circle cutter (you should end up with 2 circles per slice). Toast the brioche circles in a little butter or olive oil until crisp and golden brown.
Pour egg cream into a pastry bag and pipe onto the brioche circles. Place caviar on top and garnish with the chive rolls. Arrange on festive platters or large flat plates and serve two caviar with egg cream on crispy brioche.