In a medium saucepan of boiling water, add the potatoes and cook until soft. This will take about 15 to 20 minutes. When cooked, remove from heat, drain and set aside
Meanwhile, in another medium saucepan of boiling water, add the hake and boil for about 10 minutes. Remove from heat and drain the water. Leave to cool so you can handle it.
Once the fish is cool enough to handle, remove the skin and you will notice that the fish will just flake apart. Remove any bones that you find in the fish and discard them.
In a large mixing bowl, add the potatoes and the milk and mash really well. Now add the fish, onion, parsley and salt & pepper. With a wooden spoon, stir to combine. When it is all combined you can start making your fish cakes.
Spoon out the mixture enough to make fish cakes. Turn it into a rough ball shape and put in on the flat working surface that you are using. Flatten the top slightly and try and keep them in a circular shape. The fish cakes pictured are about 1 1/2 inches in height. Repeat these steps for remaining fish cakes.
Next, on a clean working surface, spread out the flour. With one fish cake at a time, completely coat it in the flour and put on a clean plate. Repeat for further fish cakes.
In a large skillet set over moderate heat, add the olive oil and bring to a high heat. When you put the fish cakes in the pan you want them to instantly sizzle. Cook for about 6 minutes or until it is golden brown and flip over. Continue cooking the other side for the same amount of time, or until golden brown. Repeat for whatever fish cakes you have left.
Serve straight away Alioli Sauce on the top.