Cut the asparagus spears into one inch pieces and cook in boiling water for 3-4 minutes. Remove them to the ice bath to halt the cooking process. Reserve the cooking water and 10 of the asparagus tips to use as a garnish.
Blend the remaining asparagus spears in a liquidizer with the dill, using a little of the cooking water to help get it going if needed. We need the asparagus puree to be very smooth. Season with salt and pepper.
Whip the cream until it is thick and gloopy, but not stiff.
Whisk egg whites until it is opaque white with stiff peaks.
Put 1 tablespoon of cold water into a small jug or glass. Pour the powdered gelatine into it to separate the granules. Then stir in 2 more tablespoons of hot (but not boiling) water to dissolve them into the liquid.
Mix the blended asparagus mixture with the lemon juice, gelatine mixture, and mayonnaise in a large mixing bowl.
Fold the whipped cream and then the meringue into the asparagus mousse mixture until it is fully combined. Season with lemon juice and zest, a pinch of salt, and freshly ground black pepper.
Pour the asparagus mousse mixture into small serving glasses or espresso cups and leave to gently set in the fridge for at least 2-3 hours. The mousse will remain slightly soft.
Garnish the asparagus mousse amuse bouche with a cold smoked trout and an asparagus tip, and top with a sprig of fresh dill.