Add about two tablespoons of extra virgin olive oil to a heavy skillet-- cast iron is perfect. Heat to medium and add the chopped onion. Fry until translucent and just starting to color (about 10 minutes).
Add the garlic paste and dried cayenne peppers and sauté for about a minute.
Add the tomato, tomato paste and sugar and lower to a light simmer, stirring every few minutes until the liquid from the tomatoes has reduced about halfway.
Add the cider and bring to a bubbling simmer. Simmer for about 10 minutes.
Season the hake with salt and dredge in flour. Fry in a pan of hot olive oil (it should be as hot as possible without smoking to allow for a good sear). You don't ned to fully cook the filets if they're thick-- just make sure to sear well on both sides.
Add the fish to the cider sauce, and cook at a slow simmer for another five minutes.
Serve with hearty bread or homemade potatoes, and enjoy with a bottle of Spanish cider from Asturias.