Make the shrimp
In a 2- to 3-quart saucepan, combine 2 cups of water with the wine, carrot, celery, vinegar, peppercorns, allspice, lemon zest, 2 of the bay leaves, and 1 tsp. salt. Bring to a simmer over medium-high heat, cover, reduce the heat, and simmer for about 15minutes. Add the shrimp, return to a simmer, cover, remove from the heat, and let stand for 5minutes. Drain in a colander and let cool.
Peel and devein the shrimp (discard the other solids). In a food processor, pulse the shrimp until coarsely chopped—the pieces should be pea-size. Set aside.
Melt the butter in an 8-inch skillet over medium heat. Add the lemon juice, Worcestershire, nutmeg, and cayenne and stir to combine. Remove the skillet from the heat, add the shrimp, and stir to coat. Scrape into a 10-oz. ramekin, terrine, or bowl, and smooth the surface with a spatula. Garnish with the remaining bay leaf. Cover tightly with plastic and refrigerate.
Make the salad
Toss the celery and radishes in a large serving bowl.
Put the olive oil, lemon juice, mustard, 1/4 tsp. salt, and several grinds of black pepper in a small jar. Cover and shake to combine. Season to taste with more salt, pepper, and lemon juice.
Remove the potted shrimp from the refrigerator about 2 hours before serving. Toss the salad with the dressing and parsley, and then season to taste with salt and pepper.
Lightly toast the bread. If using cocktail-size bread, halve each on the diagonal; if using sandwich-size bread, quarter on the diagonal. Mound a heaping tablespoon of the potted shrimp on each piece of toast. Serve with the salad.
The potted shrimp may be made up to 2 days ahead; keep it refrigerated until 2 hours before serving. The salad may be dressed up to 30 minutes before serving.