Mince the onion and slice the mushrooms.

Remove the vein from the shrimp if needed and chop roughly.

Heat butter in a pan over medium-low heat. Add onion and sauté for 2 minutes until softened. Add shrimp and mushrooms, cook until shrimp changes color. Sprinkle flour and stir for 2 minutes.

Add cold milk and stir. Once boiling, season with salt and pepper. Simmer for 8 minutes while stirring.

Spread the mixture flat in a tray, cover with plastic wrap, and let cool. Refrigerate for 1 hour until firm.

Divide into 6 portions, shape into oval patties with oiled hands, wrap, and freeze for 1 hour.

Mix batter ingredients in a bowl. Coat patties in batter and breadcrumbs.