1. Working with one mussel at a time, scrub well and remove beard (group of hair-like fibers), if necessary, by pulling it firmly toward hinge of shell. Transfer to a colander, discarding any with cracked shells or ones that don't close on their own when gently tapped against counter; rinse again and drain.
2. Combine mussels and wine in a Dutch oven. Cover and cook over high, shaking pot occasionally, until shells open, 5 to 7 minutes.
3. Meanwhile, place a rack in uppermost part of oven and heat broiler. Spread 1 tablespoon butter over one side of bread slices, then sprinkle with salt and place on a baking sheet. Broil until browned, about 2 minutes, then rub with halved garlic clove and set aside.
4. Use a slotted spoon to transfer mussels to a bowl (discard any that don't open) and cover tightly to keep warm. Strain cooking liquid through a fine-mesh strainer into a bowl, then rinse and dry pot. Melt remaining 1 tablespoon butter in pot over medium, then add shallot and minced garlic and cook, stirring occasionally, until softened, about 2 minutes.
5. Stir in 3/4 cup reserved cooking liquid, leaving any grit behind, and bring to a simmer. Whisk in cream and mustard and cook, stirring frequently, until sauce is slightly thickened, about 3 minutes. Stir in dill and remove from heat, then season with salt and pepper to taste. Divide mussels among bowls and pour sauce over top. Serve with garlic toasts.
Source: Hannaford fresh Magazine, March-April 2021