Method
1
Pat the beef dry with paper towels.
2
Season the beef with salt and pepper.
3
Heat the oil in a skillet over high heat.
4
Sear the beef on all sides until browned, about 6 minutes total.
5
Transfer the beef to a plate.
6
Brush the beef with Dijon mustard.
7
Refrigerate the beef until cool.
8
Finely chop the mushrooms.
9
Melt the butter in a skillet over medium heat.
10
Cook the mushrooms until their moisture evaporates, about 12 minutes.
11
Add the spinach to the skillet.
12
Cook until the spinach wilts and its moisture evaporates.
13
Season the mushroom and spinach mixture with salt and pepper.
14
Spread the mixture on a plate to cool completely.
15
Lay a large sheet of plastic wrap on the counter.
16
Arrange the prosciutto slices on the plastic wrap in an overlapping rectangle.
17
Spread the cooled mushroom and spinach mixture over the prosciutto.
18
Place the beef in the center of the rectangle.
19
Roll the prosciutto tightly around the beef using the plastic wrap.
20
Twist the plastic wrap ends to secure the roll.
21
Refrigerate the wrapped beef for 15 minutes.
22
Lightly flour the counter.
23
Roll the puff pastry into a rectangle large enough to enclose the beef.
24
Remove the plastic wrap from the beef roll.
25
Place the beef in the center of the pastry.
26
Fold the pastry around the beef.
27
Press the pastry seams closed.
28
Trim away excess pastry.
29
Place the Wellington seam-side down on a parchment-lined baking sheet.
30
Whisk the egg with the water.
31
Brush the pastry with egg wash.
32
Cut a few shallow vents in the top of the pastry.
33
Refrigerate the Wellington for 10 minutes.
34
Preheat the oven to 200°C (400°F).
35
Bake the Wellington until the pastry is golden and the beef reaches 50–52°C (122–126°F) for medium-rare, about 35–45 minutes.
36
Rest the Wellington for 10 minutes before slicing.
37
Garnish the serving platter with rosemary sprigs and cranberries.
38
Arrange the sliced Wellington on the festive platter.