Chateaubriand with White Wine and Soured Cream Sauce

I haven't eaten a chateaubrian in almost 30 years and this is the first time I've made it myself. I researched recipes on the internet and came up with this. DELICIOUS!!!!

500 g chateaubriand (matured for 28 days)
olive oil
freshly ground black pepper
sea salt
4 banana shallots, peeled and quartered
2 large garlic cloves, julienned
120 ml soured cream
150 ml dry white wine
nutmeg
1 tbsp green peppers in brine, drained
1 tsp flour
2 tbsp cold water

1. Heat to oven to 200 °C/gas mark 5.

2. Place the shallots, garlic and olive oil into the oven.

3. Heat a little olive oil in a frying pan and sear the chateaubriand for 2-3 minutes on each side. Do NOT clean the frying pan.

4. Place the meat on top of the garlic and shallots and roast for 15 minutes for rare, 17 minutes for medium rare, 18 minutes for medium (times are approximately, I'd suggest using a meat thermometer).

5. Warm a plate in the oven. Rest the meat covered in a tent of tin foil for 10 minutes.

6. Meanwhile, place the shallots and garlic in the frying pan. When they start to sizzle, add the white wine. Bring to the boil. Mix the flour and water, then add the flour-and-water mix, green peppers and the soured cream. Bring to the boil and simmer until thickend. Season with pepper, salt and nutmeg.

7. Cut the meat into slices. Serve with potatoes and sauce.