Rinse mussels under cold water, scrub shells with a brush and pull off any beards. Discard any mussels with cracked shells or that remain open when tapped.

Prepare potatoes by halving or quartering to roughly 1-inch pieces so they'll steam through quickly. Place potatoes in a medium pot, cover with cold salted water, bring to a simmer, and cook 6–8 minutes until just tender. Drain and set aside.

Seed and dice tomatoes and mince garlic and chop shallot and parsley so they are ready to add while cooking.

Sausage & Aromatics

In a large wide pot or deep skillet with a tight-fitting lid, heat the olive oil over medium-high heat. Add the sliced andouille and cook 3–4 minutes, stirring, until browned on both sides and some fat renders.

Push the sausage to one side, add the butter to the pan and reduce heat to medium. Add the chopped shallot and cook 2 minutes until softened. Add the minced garlic and cook another 30–45 seconds until fragrant but not browned. Stir in the bay leaf and thyme.

Liquids, Steaming & Finishing

Add the diced tomatoes to the pan and cook 2 minutes to soften. Pour in the white wine and stock, scraping any browned bits from the bottom of the pan. Bring the liquid to a gentle boil and let it reduce 2–3 minutes to concentrate flavor.

Add the pre-cooked potatoes to the pan along with lemon juice, kosher salt, black pepper, and red pepper flakes if using. Stir to combine.

Add the cleaned mussels to the pot in an even layer. Cover the pot with the lid and steam over medium-high heat for 5–7 minutes, shaking the pan once halfway, until mussels have opened. Discard any mussels that remain closed after 7 minutes.

Remove the lid and stir gently to coat mussels with the sauce. If the sauce seems too thin, simmer uncovered 1–2 minutes to reduce slightly. Taste and adjust seasoning with more salt, pepper, or lemon juice.

Turn off the heat and stir in the chopped parsley and an additional 1 tablespoon cold butter if you want a glossy, richer sauce. Spoon mussels, sausage, potatoes and sauce into a large bowl or shallow serving dish.