In a covered stovepot, steam the fish with the potatoes, until both are cooked through, 15 to 20 minutes. if the fish is finished cooking before the potatoes, remove the fish to a large mixing bowl while the potatoes finish cooking. strain the potatoes, reserving a cup of the cooking liquid and place them in the mixing bowl with the fish. allow the fish and potato mixture to cool completely.
While the fish and potatoes are cooling, combine the garlic, parsley, bread, salt, and pepper in a food processor. process until it’s a fine mixture. when the fish and potatoes are completely cool, add the breading and mix together.
Beat the eggs together, and then add to the fish mixture. add the parmesean and a bit more salt and pepper. mix together.
The next part is really important: you have to wash your hands, dry them, roll up your sleeves, and mix by hand! mix well, breaking apart any potatoes that havent already been incorporated into the mixture. when you’re satisfied that the mixture is fully blended, take enough into your palm to form a small ball (no larger than two inches in diameter), and then flatten the ball into a disc. set each aside, and continue until all of the mixture has been used up. if the mixture doesnt hold together well, add some of the reserved cooking liquid.
Using a heavy skillet (cast iron is best), heat the olive oil. fry the fishcakes over medium-high heat until they are golden and crispy on the outside and warm and moist on the inside, about 4 minutes per side. drain on a paper towel, and then transfer to your serving platter. garnish with sprigs of parsley and some thin slices of lemon, if desired.