Place eggs in a large pot, and cover with cold water by 1 inch. Bring to a boil. Immediately remove from heat, and let stand, covered, for 13 minutes. Drain, and run under cold water to cool.
Peel eggs; slice a bit of the white off each short side so they can sit flat. Halve crosswise, and remove yolks. Mash yolks with creme fraiche, mustard, and lemon zest. Pass through a sieve. Stir in olives. Season with salt and pepper. Spoon or pipe yolk mixture into hollow of each egg white. Garnish each egg with an olive slice.