Start this recipe by boiling the potatoes in a pan till soft. Meanwhile, Heat the olive oil in a griddle pan and add the garlic and rosemary to infuse the oil. After a minute, add the beef fillets and brown on both sides to seal. Season the beef with salt and pepper to taste, remove from the pan and place in an oven proof dish. Continue to cook the beef in the oven at 200`c, for about another 7 minutes, or to your desired taste. In the same pan with the beef juices add the beef stock pot and the red wine and reduce to a sauce. Add in the knob of butter and mix in so that you are left with a thick, glossy sauce. (Remove the garlic cloves as you will be using them in the mash) Next, make the garlic mash by draining the boiled potatoes, and mashing them quickly. Add the butter, cream, chopped parsley, fresh seasoning to taste and the whole garlic cloves from the pan used to seal the beef.Continue to mash to a smooth paste. Take the cooked beef out of the oven and leave to rest for a few minutes while you prepare the spinach. In another pan, heat the remaining double cream with the horseradish sauce till thick, then add the fresh spinach, season well with salt and pepper and cook for just a minute to wilt the spinach leaves. You are now ready to start plating your food. Take two large dinner plates and spoon the garlic mash in the middle. Next, pile the creamy horseradish spinach on top. Slice up the 2 pieces of beef fillet and arrange on the plates. Drizzle the prepared red wine sauce over the fillet and around the plate and garnish with rosemary sprigs.