Rinse mussels under cold water, discard any with cracked shells or that do not close when tapped. Trim beards and set mussels in a bowl in the refrigerator until ready to cook.

Cook aromatics

In a large, deep skillet or Dutch oven over medium heat, add 1 tablespoon olive oil and 1 tablespoon butter. When the butter foams, add the diced onion, carrot, red bell pepper, and bay leaf. Sauté, stirring occasionally, until vegetables are softened and the onion is translucent, about 6–8 minutes.

Add garlic and spice

Add 4 cloves minced garlic and 1 teaspoon red pepper flakes to the vegetables. Cook, stirring, until fragrant, about 45 seconds to 1 minute; do not let garlic brown.

Deglaze & build broth

Pour in 1 cup dry white wine and 1 cup stock, scraping up any browned bits from the pan. Increase heat to medium-high and bring to a gentle boil. Simmer for 2 minutes to cook off some alcohol and concentrate flavors.

Add mussels & steam

Add the cleaned mussels to the pot, tuck the bay leaf in if removed earlier, cover with a tight-fitting lid, and steam for 4–6 minutes, shaking the pot gently once or twice, until mussels open. Discard any mussels that remain closed after 6 minutes.

Finish sauce

Remove the lid and stir in remaining 1 tablespoon butter, 1 tablespoon lemon juice, 2 tablespoons chopped parsley, 1 teaspoon coarse salt (adjust to taste), and 1 teaspoon freshly ground black pepper. Taste the broth and adjust seasoning as needed.

Serve

Spoon mussels and broth into warmed bowls, garnish with additional parsley and a lemon wedge if desired. Reserve broth in the pot to ladle over mussels at the table.

Garlic Bread

Prepare garlic butter: in a small bowl, combine 3 tablespoons softened butter, 2 cloves minced garlic, 1 teaspoon olive oil, 1 tablespoon chopped parsley, and 1/4 teaspoon coarse salt. Mix until smooth.

Slice the baguette in half lengthwise or into 1-inch slices for individual pieces. Spread the garlic butter evenly over cut surfaces.

Lightly toast: place bread on a baking sheet and toast under a preheated broiler or in a 425°F (220°C) oven for 3–5 minutes until the edges are golden and butter is melted and bubbling. Watch closely to prevent burning.

Finish and serve: remove from oven, sprinkle with a little extra chopped parsley, slice if needed, and serve immediately alongside the mussels for dipping into the broth.