In a small saucepan, melt butter over medium heat. Add shallot, cook until tender.
Add garlic, mustard, and lemon zest, stir to combine.
Carefully pour wine into the pan, allow to cook for one minute before adding the heavy cream.
Lower heat to low and simmer for about 20 minutes, or until about half the original volume.
While sauce is simmering, prepare the scallops:
Seared Scallops:
Use a paper towel to pat scallops dry all over, season with salt and pepper. Set aside.
Using a cast iron or other heavy bottomed pan - NOT a nonstick pan! - heat over high until very hot.
Add butter to the pan, allow to melt.
Add scallops to the pan, each one laying on one of the flat sides. Cook for about 2 minute, or until a nice crust forms.
Flip the scallops, cook for another 2 minutes.
Serve on a puddle of the cream sauce.
