Stuffed beef fillet with green beans and celery mashed potatoes

Ingredients:

Mashed potatoes with celery

• 3 large Idaho potatoes, cut into 2cm cubes, soak in water until ready to use
• 1 large celery root, cut into 2cm cubes.
• 1 - 1.5 cups heavy cream
• 110 g chilled butter, cut into pieces

Green beans

• 220 g green beans, ends removed
• Extra-virgin olive oil
• 2 cloves garlic, crushed
• A pinch of red pepper flakes

Beef tenderloin

• Extra-virgin olive oil, for greasing
• Half a small red onion, diced
• 6 brown mushrooms, finely chopped
• 6 shiitake mushrooms, finely chopped
• 1/4 tbsp. dry sherry
• 3/4 cup crumbled blue cheese, such as Stilton
• 1/3 cup plain breadcrumbs
• Half a bunch of chives, chopped, plus extra for serving
• Half a bunch of parsley, chopped
• 2 filet mignon steaks, 5 cm thick.
• Rapeseed oil (canola) for frying
• Half a shallot, chopped
• 1/4 cup red wine
• 0.5 - 3/4 cup beef broth
• 1 tbsp Dijon mustard
• Butter, for the sauce

Preparation:

1. Mashed potatoes with celeryPlace the potatoes in a saucepan large enough to hold the celery root and potatoes. Add enough water to cover the vegetables by 2 inches (5 cm) and season generously with salt.
   
   Bring to a boil and simmer for about 10 minutes. Add the celery root and simmer until soft. Drain the water.
2. Pour the cream into a small saucepan and bring to a simmer. Meanwhile, puree the celery root and potatoes with a vegetable mill into a large bowl. Add a quarter of the hot cream and 2 knobs of butter. Stir vigorously until the cream and butter are thoroughly combined. Repeat with the remaining cream and butter. Taste and add salt if necessary. Keep the puree warm until ready to use.
3. Boil the beansBring a large saucepan of salted water to a boil over high heat. Place a bowl of well-salted ice water nearby.
   
   Add the beans to the boiling water and cook until tender but still crisp, 5-7 minutes. Drain and immediately plunge the beans into salted ice water. Once cool, drain and set aside until ready to serve.
4. Preheat oven to 190°C.
5. Filling: Grease a medium skillet with olive oil and place over medium heat.
   
   Add the onion, season with salt, and cook until softened and fragrant, 4 minutes. Add the mushrooms and shiitake mushrooms and cook until they release some liquid and then become dry. Add the sherry and cook until the pan is almost dry. Remove from heat and let cool. Stir in the blue cheese. breadcrumbs, green onions, and parsley and mix. Transfer the filling to a pastry bag and set aside.
6. Stuffed beef filletInsert a paring knife into the steak and wiggle it back and forth to create a pocket. Repeat with the second steak, then spoon the filling into each pocket. Sprinkle the steaks with salt.
   
   Grease an oven-safe frying pan with canola oil and place over medium heat. Sear the steaks on both sides and return to the oven for 5 minutes. Remove the steaks from the pan and set aside to rest.
7. Sauce: Return the skillet to the stovetop over medium heat.
   
   Add the shallots and season with salt. Fry until soft. Add the red wine and reduce by half. Add the beef broth and mustard. Bring to a boil, then reduce the heat. Stir in a little butter.
8. Green beans: Grease a large skillet with olive oil.
   
   Add the garlic and red pepper and cook over medium heat. When the garlic is golden and fragrant, remove and discard. Add the beans to the pan and cook until heated through and coated with oil. Transfer the beans to a serving platter and season with salt.
9. Drizzle each steak with a little sauce and serve with mashed potatoes and beans. Garnish with fresh green onions before serving.