Rolling and stuffing the meat is easier than it looks.
Open it flat, like you would a book.
Spread the creamy spinach-and-leek filling evenly over the beef, leaving a 1/2-inch border around the edges.

Credit: Photo: Hector Manuel Sanchez; Prop Styling: Buffy Hargett Miller; Food Styling: William Smith
Roll up the beef in a jelly-roll fashion.
Finally, using kitchen twine, secure beef by tying at 2-inch intervals.
Brush all sides of the beef evenly with olive oil; sprinkle with salt and pepper.
Your holiday dinner guests will be impressed by thistasty display.
Ingredients
Beef
3(10-oz.)
beef tenderloin, trimmed
1tablespoonextra-virgin olive oil
Sauce
2tablespoonsunsalted butter, divided
1tablespoonolive oil
2(8-oz.)
Drain spinach well; press between paper towels to remove excess moisture.
Melt butter in a medium-size straight-sided saucepan over medium.
Add leeks and garlic, and cook, stirring occasionally, until softened, about 4 minutes.
Add flour, and cook, whisking constantly, 3 minutes; whisk in cream until smooth.
Add spinach, and cook, stirring occasionally, until mixture is very thick, about 5 minutes.
Remove from heat, and let cool 10 minutes.
(The cut should be within 12 inch of other side.)
Open top cut piece, as you would a book, and lay flat.
Place between 2 sheets of plastic wrap.
Spread leek-spinach mixture evenly over Beef, leaving a 12-inch border around edges.
Roll up Beef, and tie with kitchen twine, securing at 2-inch intervals.
Brush evenly with olive oil; sprinkle with remaining 1 teaspoon salt and 12 teaspoon pepper.
Place Beef on a wire rack set over a rimmed baking pan.
Bake in preheated oven 30 minutes.
Increase oven temperature to 450F (do not remove from oven).
Bake until a meat thermometer registers 125F, about 20 minutes.
Remove from heat, and let stand 30 minutes before slicing.
Add mushrooms, and cook, stirring once or twice, until lightly browned, 5 to 6 minutes.
Add shallot; cook, stirring constantly, until tender, 1 to 2 minutes.
Stir in wine; cook, stirring constantly, 2 minutes.
Stir in broth; reduce heat to medium, and simmer, stirring constantly, 5 minutes.
Stir in mustard, rosemary, salt, and pepper, and cook 1 minute.
Remove from heat, and stir in remaining 1 tablespoon butter until combined.
Serve Sauce with Beef.