Step 1: Make the Lemon-Herb Aioli

1. In a small bowl, whisk ½ cup mayonnaise with the zest and juice of 1 lemon, 1 tsp black pepper, and 3 Tbsp chopped parsley until smooth.
2. Set aside or refrigerate until ready to serve (can be made up to 2 days ahead).

Tip: Adjust lemon juice for desired tanginess; stir well to incorporate parsley evenly.

Step 2: Prep the Mussels

1. Debeard and clean 2 lb mussels thoroughly under cold water, scrubbing shells and removing beards.
2. Discard any mussels with cracked shells or that don’t close when tapped.

Tip: Soak mussels in cold water for 10 minutes to remove sand; store in a bowl with a damp cloth in the fridge until cooking.

Step 3: Sauté the Vegetables

1. In a large skillet, melt 2 Tbsp butter over medium heat.
2. Add 2 thinly sliced celery stalks and 2 thinly sliced leeks; sauté until tender, 3–4 minutes.
3. Add 1 minced garlic clove and sauté until fragrant, about 1 minute.

Tip: Slice leeks and celery thinly for quick cooking; rinse leeks well to remove dirt.

Step 4: Build the Broth

1. Stir 1 Tbsp tomato paste into the skillet and cook for 1 minute.
2. Add 2 lb cleaned mussels and toss gently with the vegetables.
3. Pour in 1 cup dry white wine and ½ cup seafood broth or water; bring to a simmer over medium heat.
4. Season with salt, black pepper, and ⅓ cup chopped parsley.

Tip: Stir tomato paste thoroughly to avoid clumps; use a large skillet to fit mussels comfortably.

Step 5: Steam the Mussels

1. Cover the skillet and simmer for 5–6 minutes until most mussels have opened.
2. Discard any mussels that remain closed.

Tip: Shake the skillet gently during cooking to distribute heat; check early to avoid overcooking.

Step 6: Serve

1. Divide the mussels and broth with vegetables between two bowls.
2. Serve immediately with herby shoestring fries and lemon-herb aioli on the side.

Tip: Serve with a slotted spoon for mussels and a ladle for broth; keep fries separate to maintain crispness.