Creamed Spinach–Stuffed Filet Roast

Name: Creamed Spinach–Stuffed Filet Roast
Ingredients: 3 tablespoons unsalted butter; 1 small shallot, minced; 1 garlic clove, minced; 1/4 cup all-purpose flour; 1 1/2 cups heavy cream; Three 10-ounce packages thawed frozen chopped spinach, excess water squeezed out; 1/4 cup freshly grated Parmigiano-Reggiano; 1/4 teaspoon freshly grated nutmeg; 2 teaspoons fresh lemon juice; Kosher salt; Pepper; One 3-pound center-cut filet mignon, butterflied 1/4 inch thick (have your butcher do this); 2 tablespoons extra-virgin olive oil