Not quite a stew or soup, but close-ish to a bouillabaisse, this brown butter poached fish with mussels is perfect as-is but also a good blank canvas for whatever you're feeling moved by. Chili flake to the browned butter? Sliced fennel to sizzle along the lemon and garlic? A small can of crushed tomatoes to the broth? While I like a big thick cut slab of toast smeared with aioli to dunk, this would also be fabulous served over herby rice or buttered linguini.
1. Thinly slice half the lemon and set the other half aside (for juicing later).
2. Heat butter in a large skillet over medium–high heat. Once the butter melts and starts to foam up, add olive oil to prevent it from burning. Add garlic and lemon slices and season with salt and pepper. Cook, swirling the skillet occasionally until the garlic and lemons are both softened and starting to brown, 3 to 5 minutes.
3. Add wine and thyme (if using) to the skillet and let it simmer and reduce by about half, 2 to 3 minutes. Add 2 cups of water and season with salt and pepper. Bring to a simmer and gently add fish and mussels to the skillet. Season fish with salt and pepper and reduce heat to medium. If you have a lid for the skillet (or a different pot that would fit), place it on top. Otherwise, use something like a sheet tray.
4. Cook, shaking the skillet occasionally, until the fish is cooked through and the mussels are fully opened, 3 to 4 minutes. Remove from heat, then squeeze some of the lemon over everything. Taste the broth and adjust with more salt, pepper and lemon as you like.
5. Serve with herbs sprinkled over, next to a big bowl of aioli and plenty of thick, fabulous bread for sopping up the broth.