To de-beard the mussels, just pull off the hair-like bits coming out of the shell.

 

8 1/2-inch-thick slices sourdough bread (each about 2 x 4 inches)
6 tsp. olive oil
4 tsp. chopped garlic

1 1/2 cups chopped seeded plum tomatoes
1/2 cup chopped fresh Italian parsley
3 pounds mussels, scrubbed and de-bearded

 

Preheat oven to 375°F.  Arrange bread on baking sheet. Combine 4 tsp. oil and 2 tsp. garlic in bowl. Using fork, mash to course paste. Spread over bread. Bake until crisp, about 10 minutes.  Heat 2 tsp. oil in a heavy large pot over medium-high heat. Add 2 tsp. garlic; sauté 2 minutes. Add tomatoes and parsley. Reduce heat; simmer until sauce thickens, stirring often, about 10 minutes. Season with salt and pepper. Add mussels; increase heat to high. Cover; cook until mussels open, about 7 minutes (discard any mussels that do not open). Divide mussel mixture among soup bowls.  Place toasts at edge of each bowl.