In a large dry skillet, toast mustard seeds over medium heat until they begin to pop and release their aroma, approx. 30 seconds. Transfer seeds to plate to cool.
In the same skillet, add olive oil and sauté shallots until translucent. Add sherry vinegar and water, simmer until liquid has reduced to 1 tablespoon (10-12 mins). Add heavy cream to the skillet and simmer until mixture is thick enough to coat the back of a spoon. Remove from heat and let sit to cool to room temperature.
In a large bowl, mix toasted mustard seeds, softened butter, shallot mixture, and Mustard Orléans. Just before serving, bring a large pot of salted water to a boil. Cook the beans until bright green and just tender; strain and dry beans. Top cooked beans with mustard seed butter and toss to coat. Season to taste with salt and pepper.
Note: The Mustard Orléans Butter can be made in advance and tossed with warm green beans just before serving. Butter will last up to three days refrigerated and one month in the freezer.