For the roast fillet of beef
Place the fillet on a chopping board. With a sharp knife, slice it lengthways along the centre, butterfly-style, keeping it in one piece so that it opens like a book.
Cover with cling film and reserve on a tray in the fridge while you prepare the filling.
In a food processor, finely chop the mushrooms, garlic and herbs together.
Evenly spread the mixture onto a large roasting tray and place the garlic bulb in one corner.
Place the tray of mushrooms and whole garlic bulb into a cold oven and then turn the temperature to 220⁰C.
After 25 minutes remove the tray from the oven. Keep the garlic bulb to one side, ready to make the sauce. Allow the mushroom mix to cool.
Cut two even pieces of Saint Agur blue cheese into strips 2cm wide. Keep the remaining Saint Agur Blue Cheese for the sauce.
Remove the fillet of beef from the fridge and place it on a chopping board so the longest edge is facing you. Season with a pinch of salt and pepper and evenly spread the mushroom mixture all over but leaving a gap of 1cm around the edge.
Place the Saint Agur blue cheese pieces along the fillet 5cm in from the edge closest to you.
Now roll the fillet away from you and secure it with 3 lengths of string.
Season the outside of the beef fillet with salt and pepper.
In a large frying pan on a high heat, sear the stuffed and rolled beef fillet until golden all over. This should take 4-5 minutes.
Place the seared beef fillet into a large shallow oven tray and roast in the preheated oven for 30 minutes.
Once out of the oven, lightly cover the fillet with tinfoil and leave it to rest for 30 minutes. Meanwhile prepare the sauce and your choice of vegetable accompaniments.
For the Saint Agur Blue Cheese and roast garlic sauce
Slice the top off the roasted garlic bulb and squeeze out the softened cloves of garlic onto a chopping board. Crush with the back of a fork to make a garlic purée.
Place the garlic purée, Saint Agur blue cheese, crème fraîche and cayenne pepper into a small saucepan on a high heat.
Bring the ingredients to a gentle simmer, stirring with a spatula or wooden spoon to combine evenly and then remove the pan from the heat.
Once the beef has rested for 30 minutes it is ready to carve and serve. Return the sauce to the heat to warm through and serve with your choice of vegetables.