Carefully peel your hard-boiled eggs, then slice them in half lengthwise.

Remove the yolks and place them in a medium-size bowl. Mash them with a fork until all that's left is a fine crumble.

Add the crème fraîche, mustard, and salt. Stir together until smooth.

Transfer the mixture to a piping bag fitted with a tip and pipe into the egg whites. Top with caviar and chives, then serve immediately.