Preheat the oven to 190°C.
Line a baking tray with foil, grease with oil, and bake the trout for 12 to 15 minutes.
Remove the skin and flake the fish into a sieve, discarding any bones.
Melt butter in a pan and fry the onion for 3 minutes until colored.
Stir in the 40g of flour and cook for 30 seconds.
Add the milk gradually and stir for 5 minutes until the mixture thickens.
Off the heat, beat in tomato purée, tarragon, mustard, cream, salt, and pepper.
Fold in the trout flakes and chill in the fridge for at least 5 hours until solid.
Form the mixture into 15 small croquette shapes.
Set up bowls with 3 tablespoons of flour, beaten eggs, and the almond-breadcrumb mix.
Coat each croquette in flour, then egg, then the breadcrumb mixture.
Chill the breaded croquettes in the fridge for 30 minutes.
Heat sunflower oil in a large pan to 180°C.
Fry the croquettes in batches for 3 minutes until golden brown.
Drain on kitchen paper and serve with lemon wedges.