Slice the fish fillet diagonally. Marinate with salt, white pepper, rice wine & corn starch.
Fry the spices
In a wok (or a deep frying pan), fry dried chilli and Sichuan pepper in oil over a low heat until fragrant (do not burn them). Chop coarsely when cooled. Set aside.
Cook the vegetable
In the same wok, heat up oil over a medium heat, stir in celery. Cook for 1.5 minutes or so (30 seconds if using bean sprouts instead). Transfer to a serving bowl. Set aside.
Make the broth
Heat up oil in the wok, fry garlic, ginger and spring onion. Add Sichuan chilli bean paste and chilli powder. Pour in water (or chicken stock). Bring it to a full boil.
Cook the fish
Gently place the fish slices into the wok. When cooked, pour the fish and the soup onto the vegetable.
Garnishing
Top with fried spices and coriander. Heat up oil then pour over to sizzle the spices. Serve immediately with plain rice.
Notes
1. You may use catfish, cod, sea bass, pangasius, etc.2. I use two different types of Sichuan peppercorn in this dish: the red, regular Sichuan pepper and green ones. Please feel free to use whatever is available to you.3. Different brands of Sichuan chilli bean paste (aka spicy Doubanjiang/辣豆瓣酱) may vary in saltiness, hotness and texture. Adjust the volume accordingly. Best to use Pixian Douban (郫县豆瓣), a well-known variety, which needs to be coarsely chopped prior to cooking.