Green Beans with Mustard Cream

2 tablespoons mustard seeds
4 shallots, sliced
2/3 cup sherry vinegar
1/4 cup water
1/2 cup cream
1 stick butter, softened
1/4 cup whole grain mustard
4 1/2 pounds green beans, cooked crisp tender

Toast seeds until they pop. Allow to cool.
Add shallots, vinegar and water and simmer until reduced to 1 tablespoon.
Add cream and allow mixuture to thicken slightly. Cool to room temperature.
Add butter, mustard, and toasted seeds.
Toss with beans.