"Fish" no Kasuzuke is a traditional way to serve black cod or Gindara, which Nobu of Nobu fame has sort of turned into a high cuisine. The recipe is actually quite simple, though fresh sake kasu, or sake lees, can be hard to source. I buy mine at the local Japanese grocery in slurpy giant bags for cents on a pound. The below kasuzuke marinade works fine without the heat treatment, but the marinating time may need adjustment depending on your taste. 

6 oz fresh fish fillet of choice - For buttery kasuzuke, use butterfish/black cod/sable, mackerel, salmon, snapper or any tender, and fatty fish of choice... otoro! Some recipes actually include butter, but with a nice oily fish there really isn't the need.
1/2 cup sake kasu, stores for ages in the fridge.
2 tbsp brown or white sugar
3 tbsp shiro miso
2 tbsp sake
1 tbsp mirin - If you have the dry sake kasu, use the mirin to rehydrate.
1/4 cup water

Salt fish lightly, and rest for at least several hours or overnight in the fridge. Dry. Bring sugar, sake kasu, sake and mirin to a boil. Take off the heat and add miso, stirring in a little water as needed to make a thick, creamy paste. Let cool and coat fish with marinade, cover, and refrigerate 2-7 days - I like the minimum. While waiting for your fish to "cure", read some of this. Scrape off marinade. Gently bake fillet at relatively low heat for several minutes on each side, then turn on the broiler at the last minute to crisp the skin.

An alternate to the strong flavor of kasuzuke is misozuke, a similar pickling sauce omitting the sake kasu and thus having a less overwhelming flavor. Here's Nobu's recipe using a saikyo miso, essentially shiro or white miso with large proportion of white sugar added.

I have also seen sake kasu used to marinate fish roe, soup, various vegetables, or added to rice like a condiment. Some additions to the basic sauce include citrus peel or ginger depending on the main ingredient. Tsukemono includes wasabi to a mix of wood ear and cauliflower. Here are some other recipes in English even.