8T unsalted butter
1 med onion, finely chopped
2 garlic cloves, minced
6 tablespoons all-purpose flour
1 1/2 cups milk
1/4 teaspoon cayenne pepper
2 teaspoons dry mustard
4 ounces sharp white cheddar cheese, shredded (1 cup)
2 tablespoons fresh lemon juice, plus freshly grated zest of 1 lemon
2 teaspoons Worcestershire sauce
10 ounces lump crabmeat, picked over
2 tablespoons coarsely chopped fresh flat-leaf parsley
Coarse salt and freshly ground pepper
Baguette slices, toasted, for serving
1 loaf rustic bread (about 1 pound), trimmed of crust and torn into 1-inch pieces (4 to 5 cups)