At least 24 hours before making your croquettes, place the cod in a bowl of water in the fridge. Change the water at least three times.
After the cod has been in the water for at least 24 hours, remove it, dry it with a napkin and shred it into tiny pieces, making sure to remove any bones.
In a medium frying pan, add 2 tbsp of oil and heat over medium heat. Once hot, add your diced onions and garlic. Cook for about 5 minutes, until the onion is translucent.
Add the shredded cod afterwards, saute for about 5 minutes and remove from the heat and set aside.
In a large saute pan over medium heat, add butter and 2 tbsp of olive oil. Heat until the butter starts to foam. Add the flour to make a roux and continuously stir, until it becomes a golden color. Next, add the whole milk slowly until it is well incorporated.
Once the milk is incorporated, add the cod back in and season the mixture with garlic powder, salt, nutmeg, and black pepper. Stir to combine everything together. Remove the mixture, alace it in the fridge and allow it to cool (for at least 4 hours or overnight).
Once chilled, scoop out about 2 tbsp of filling and roll into a ball or log. Dip the croquette into the flour and then into an egg wash, and after into the bread crumbs or plantain chip crumbs and set aside. Repeat until you have no more filling left.
In a deep fryer or on a pan, heat up oil to about 350°F. Place the croquetas in the oil for about 2-3 minutes, until golden brown. Transfer to a plate line with a paper towel.
To make a dill aioli, combine mayo, fresh dill, lemon, salt, pepper, and a diced garlic. Stir until it’s well incorporated. Serve together with the croquettes.