Glazed Haricots Verts with Pickled Shallot-Walnut Relish

Place shallots and mustard seeds in a heatproof medium bowl. Combine vinegar, water, sugar and salt in a small saucepan. Bring to a boil, stirring to dissolve the sugar and salt. Pour the pickling liquid over the shallots. Top with a small plate. Set aside at room temperature for at least 30 minutes and up to 4 hours, or refrigerate for up to 2 days.

Place a large bowl of ice water near the stove. Bring a large pot of water to a boil. Cook beans just until crisp-tender, 1 1/2 to 2 minutes. Drain and transfer to the ice water until cold. Drain, pat dry and transfer to a large bowl.

Drain the shallots, reserving the pickling liquid, then return them to the bowl. Stir in walnuts, parsley and 1 tablespoon of the pickling liquid.

Bring 1/2 cup pickling liquid to a boil in a small saucepan over medium-high heat. Boil until reduced by half, 2 to 4 minutes. Whisk in butter, one cube at a time, until the sauce is thickened. Pour the sauce over the beans and toss to combine. Transfer to a serving platter and top with the shallot-walnut relish.