Carefully clean, rinse and pat dry the hake. Sprinkle the fillets lightly with salt.
Heat the oil over medium-high heat in a large, heavy skillet. Add the garlic and cook until the garlic just begins to color, about 5 minutes. Sprinkle the flour over and mix thoroughly, 1 to 2 minutes. Add 1 cup of water, the clam broth or juice, wine, parsley and salt to taste. Decrease the heat to medium and cook the sauce, stirring occasionally, until the sauce is slightly thick or just barely coats the back of a wooden spoon, about 5 minutes. You can add more cold water to loosen up the sauce if necessary.
Add the hake to the pan, skin-side up, in a single layer. Cook the hake fillets in the sauce for 2 minutes, swirling the pan constantly and sliding the pan on and off the fire until the hake fillets give off some of their gelatin and emulsify with the rest of the sauce. Flip the hake fillets once and cook until the fish is opaque but not overcooked, another 2 to 3 minutes on the other side. The sauce should be very light green and slightly thick but still loose and light. Serve immediately.