Beat crème fraiche and cream cheese with a hand mixer until fluffy. Mix in half of the shallot and dill. Divide in two.

Remove the layer of skin from the salmon and discard. Place salmon in a food processor or blender with lemon juice, remaining shallot and dill, onion, and one half of the crème fraiche mixture. Process salmon until smooth, adding more lemon juice if needed.

Season mousse to taste with salt and pepper.

Line a loaf pan or mold with plastic wrap. Fill the plastic wrap lined mold with hot water for a few minutes to make the plastic form to the mold. Empty water and allow to air dry. Lightly spray the lined mold with non-stick cooking spray.

Spread remaining half of crème fraiche mixture evenly in bottom of mold. Place in freezer to firm, about 15 minutes.

Spread salmon mousse evenly over crème layer. Cover with a layer of plastic wrap pressing the wrap directly on the mousse.

Hold in the fridge or freezer until ready to serve.

When ready to serve place mold in the freezer for about 30 minutes. Remove plastic wrap and invert on to a serving platter. Slowly lift the mold and gently peel off the plastic wrap.

Salmon mousse freezes very well. If mousse was held in the freezer, dip mold in warm water for a few seconds. Invert frozen mousse onto serving plate. Gently remove plastic wrap and allow mousse to thaw before serving.

Decorate the top with fronds of fresh dill and dollops of caviar.