Rinse the mussels in cold water and scrub off any grit. Pull off the stringy beards by tugging them toward the hinge end. Tap any open mussels on the counter; discard any that do not close, as well as any with cracked shells. Keep the cleaned mussels in a bowl in the fridge until cooking.

Pat the shrimp dry with paper towels and season with the salt and pepper.

Heat 1 tablespoon olive oil in a 12-inch deep skillet or Dutch oven over medium-high heat. Add the shrimp in a single layer and sear for about 1 minute per side, just until pink on the outside. They will finish cooking later. Transfer to a plate.

Lower the heat to medium. Add the remaining 1 tablespoon olive oil and 1 tablespoon butter. Cook the shallot for 2 minutes until soft, then add the garlic and red pepper flakes and stir for 30 to 60 seconds until fragrant, without browning the garlic.

Add the cherry tomatoes and cook for 2 minutes until they start to soften. Pour in the white wine, scrape up any browned bits, and simmer for 2 minutes to cook off some of the alcohol. Add the broth and bring to a lively simmer.

Add the mussels, cover with a tight-fitting lid, and steam for 4 to 6 minutes, shaking the pan once or twice, until most of the shells have opened.

Return the shrimp and any juices to the pan, tucking them into the broth. Cover and cook for 1 to 2 minutes until the shrimp are opaque and just cooked through.

Turn off the heat. Stir in the remaining 2 tablespoons butter, the lemon juice, and most of the parsley. Discard any mussels that stayed closed. Taste the broth and add salt only if needed.

While the mussels steam, brush the bread slices with olive oil and toast them in a grill pan or under the broiler until golden. Rub with the cut garlic clove if you like.

Serve straight from the skillet or in shallow bowls, with lemon wedges, the remaining parsley, the grilled bread for dipping, and an empty bowl for shells.