Open the mussels by pouring hot water over them in a bowl, or steaming them slightly in an open pan with a little water. Remove from the shells and clean, then chop finely or whiz in a food processor, leaving the mixture a little chunky.
With a fork, whisk together the egg, flour, baking soda, salt and pepper to taste and the herbs. Add the chopped mussels and chill the mixture for 1 hour if you have the time.
Heat the oil gently in a heavy-based frying pan and fry large tablespoons of the mixture until golden brown on both sides.
Drain on paper towels and serve with lemon wedges.