Preheat oven to 425°F. Line baking sheet with parchment paper.
Season beef with salt and pepper.
Whisk together butter and mustards.
Coat beef with butter mixture.
Roast for about 35-40 minutes until a thermometer reads between 135°F-138°F (rare to medium-rare). Cooking time will vary depending on the thickness of the cut.
Allow meat to rest for 15-20 minutes before slicing.
Right before serving, prepare the sauce.
In a small saucepan, whisk together 2 1/2 tablespoons stone-ground mustard with 1 cup heavy whipping cream.
Bring to a simmer and remove from heat. Immediately serve.