Step 1

Prep your ingredients before you start cooking: First, peel and set aside 1 garlic clove for the mayo, then peel and smash remaining 6 garlic cloves.

Step 2

Pick any leaves from 1 celery heart. Thinly slice celery heart crosswise (making little half-moons) until you have about 1¼ cups. Set aside ¼ cup chopped celery along with leaves for serving.

Step 3

Peel 3" piece ginger. Set aside a ½" nub for later, then cut remaining piece crosswise into thin slices.

Step 4

Rinse 4 lb. mussels in cold water and remove the “beard” (that thread-like piece attached to the side of the shells) by tugging firmly. If any mussels are open and don’t close when tapped, discard. Drain and transfer to a large bowl.

Step 5

Heat 3 Tbsp. butter in large pot or Dutch oven over medium. Add smashed garlic, sliced ginger, and 1 cup chopped celery and cook, stirring often with a wooden spoon, until garlic is golden, 5–8 minutes.

Step 6

Add ½ cup mirin, ⅓ cup sambal, and ¼ cup soy sauce and bring to a simmer. Cook, stirring once or twice, until mixture is reduced by about half, about 5 minutes.

Step 7

Add 28-oz. can tomatoes and juices to pot, breaking up tomatoes with your hands as you add them, and bring to a simmer. Season lightly with salt. Let simmer, uncovered, to allow flavors to meld, about 5 minutes.

Step 8

Add mussels to pot and stir into tomato mixture. Cover pot and cook, stirring once halfway through, until mussels are opened and fully cooked, 6–8 minutes.

Step 9

Meanwhile, finely grate reserved garlic clove and ½" nub ginger into a small bowl. Add ½ cup mayonnaise and remaining 1 Tbsp. soy sauce and stir to incorporate.

Step 10

Preheat broiler with rack in top position. Cut ½ baguette in half lengthwise and toast, cut sides up, directly on oven rack, until bread is golden across the surface, about 1 minute. Let cool.

Step 11

When mussels are opened, uncover and remove from heat. Ladle into shallow bowls along with tomato mixture. Top with reserved chopped celery and leaves.

Step 12

Tear bread into pieces and smear toasted sides with mayonnaise mixture. Serve with mussels for soaking up liquid.