Start with the filling, heat some Olive oil and sweat the onions
Add the garlic and the red peppers followed by all the herbs
Switch the flame off and add the cheese to melt
If the cheese is not melting, switch the heat back on but be careful not to cook the herbs
Add a tsp each of both the mustards and leave to cool
Remove the net from the lamb leg and using a sharp knife, make horizontal cuts to butterfly it.
Dry the lamb with a paper towel and sprinkle with salt and pepper and place it on a board, fat side down.
Mix the other two mustard types together and spread some on the inside of the lamb
Once the filling is cooled, spread it all over the lamb and roll it up
Using butcher's string or twine, truss the roast (see video)
Using the remaining mustard, spread it all over the lamb, cover with cling wrap and marinate
Heat your oven to 450 degrees and heat your roasting pan and add the lamb to it.
Cook it for 25 mins, then reduce the temp to 350 and add the mirepoix of vegetables to it
For medium well, cook for 45 mins and well done for 90 mins