Shorshe Ilish

Step 1

Pat 4 hilsa fish fillets completely dry with paper towels — removing surface moisture allows the spices to adhere properly. Set aside on a plate.

Step 2

In a small dry skillet over medium heat, toast 2 tablespoons yellow mustard seeds and 1 tablespoon black mustard seeds, stirring constantly, until fragrant and just beginning to pop, about 2-3 minutes. Transfer to a spice grinder or mortar and pestle and grind to a coarse paste — you want some texture, not a powder. Transfer to a small bowl.

Step 3

To the ground mustard, add 0.5 teaspoon turmeric powder and 1 teaspoon salt. Stir in 2 tablespoons of water to form a paste. Coat each fish fillet evenly on both sides with this mustard paste and set aside for 15 minutes to marinate.

Step 4

While the fish marinates, slice 1 medium yellow onion into thin half-moons. Slice 3 fresh green chilies lengthwise into strips, keeping seeds intact for heat. Peel and finely grate a 1-inch piece of fresh ginger on a microplane. Peel and mince 4 garlic cloves into tiny pieces.

Step 5

Set a 12-inch shallow cooking pan or wide skillet over medium-high heat and pour in 4 tablespoons of vegetable oil. When the oil shimmers and just begins to smoke at the edges, carefully lay each marinated fish fillet skin-side down in the oil. The oil should sizzle immediately and loudly — if it's silent, wait another 10 seconds. Sear for 4-5 minutes without moving the fish, until the skin is deeply golden and crispy. You'll smell a rich, nutty aroma. Gently flip each fillet and sear the other side for 2-3 minutes until just cooked through. Transfer the fish to a clean plate.

Step 6

Reduce heat to medium. In the same pan with the remaining oil and browned bits, add the sliced onions. Sauté, stirring often, until the onions turn soft and translucent, about 3-4 minutes. You should see them soften and become slightly golden at the edges.

Step 7

Add the minced ginger and garlic to the onions and stir constantly for 30-45 seconds until fragrant — the aromatics will perfume the oil and you'll smell the garlic cook. Do not let them brown; lower heat slightly if they begin to color.

Step 8

Sprinkle in 1 tablespoon mustard powder, 0.25 teaspoon turmeric powder, and 0.5 teaspoon red chili powder. Stir vigorously for 10-15 seconds to bloom the spices in the hot oil — this releases their essential oils and prevents clumpy mustard paste.

Step 9

Pour in 0.75 cup of water, scraping the bottom of the pan with a wooden spoon to deglaze and incorporate all the browned bits. Add the green chili strips. Bring the sauce to a simmer over medium heat — you'll see gentle bubbles breaking the surface. Taste and adjust salt as needed.

Step 10

Carefully lay the reserved fish fillets back into the simmering sauce, skin-side up. Reduce heat to medium-low and gently simmer uncovered for 5-7 minutes, until the fish is fully cooked through and the sauce has thickened slightly — it should coat the back of a spoon. The sauce should be fragrant and glassy, not watery. Baste the fish with the sauce two or three times during cooking.

Step 11

Transfer the shorshe ilish to a serving platter or divide among 4 shallow bowls, spooning the mustard sauce and onions generously over each fillet. Scatter 3 tablespoons of fresh cilantro leaves over the top for brightness. Serve immediately while the fish is still steaming — the silky flesh and pungent mustard sauce are best eaten warm.