Season pork tenderloin with salt, pepper, paprika and French mustard. Heat a pan, add olive oil and sauté the tenderloin well. Cut potatoes in cubes and boil in a pot.
When meat is nicely browned, take off the pan and add onion and leek to sauté them. Next, add mushrooms- cut in slices- and chopped garlic.
When vegetables are cooked, add meat and reduce with red wine and Worcestershire sauce. Cover pan.
Glaze and finish off with chopped rosemary, salt and pepper. Set aside.
When potatoes are cooked, strain well. Add butter and whipping cream stirring well with a whisk. To finish, add I tsp. olive oil, salt, pepper and chives.
When you want to boil roots, always start by boiling with cold water. This will preserve their starch and they will be cooked correctly.