Melt butter in a small saucepan over medium heat until melted, then pour 2/3 into a bowl and set aside.
Add the shallot, garlic and lemon rind to the pan and let it cook gently for 3 to 5 minutes until soft and translucent (it should not brown). You will only need to stir it occasionally.
Meanwhile, remove the skin off the trout and discard. Use your hands to remove the flesh and place into a bowl, being careful to avoid the bones (you will be able to pull the flesh off the bones easily). Use a fork to flake the flesh. Discard the bones.
Pour the shallot butter mixture into the bowl with the trout.
Add lemon juice, cayenne pepper, creme fraiche, cream and herbs. Stir gently until well combined. Do a taste test and add salt and pepper if required. You may not need salt as smoked trout is often salty (I only add a tiny pinch).
Spoon into jars or ramekins (1 large, 2 medium or 4 small) and smooth the surface.
Pour over the reserved butter until the top is covered.
Place in the refrigerator to set. (Note: Original recipe set to freeze it for 5 - 10 minutes first but I found that this caused the surface of the butter to crack).
This can be served on the day you make it, but it gets even better with time. It can be made up to a week in advance.
Serve with fresh or toasted bread.