Skin and debone the fish. With your hands cut it into very small pieces and place them in a large bowl.
Add in the mashed onion, the spearmint, the dill and season with salt and pepper. Mix well all the ingredients together. Add the flour, stirring constantly until the desired thickness is achieved. If the mixture thickens further, pour into some beer. Set aside in the refrigerator for 1 hour.
Prepare the oil in moderate heat.
Take the mixture with a spoon from the bowl forming small balls and fry. Serve with “Skordalia” (Greek potato and garlic dip)