My homemade cooking

500 gr mussels (approx. 2 kg with shell)
100 gr fish or peeled prawns (if mussels turn out to be small)
1 medium onion finely chopped
400 ml stock left from cooking mussels
200-300 ml milk
2 teaspoons ketchup
10 tablespoons brown rice flour (or regular flour if not making a gluten free recipe)
6 tablespoons olive oil
Tabasco to taste
Rice crumbs (or [...]