In a large saute pan over high heat place oil, add mushrooms and sear well. Add the shallots and continue to cook until mushrooms are tender and any liquid has evaporated. Place mixture in a food processor and pulse until finely chopped. Refrigerate until completely cool.
In a stainless mixing bowl place ground lamb, mushrooms, and herbs. Mix until well combined and season with salt and pepper.
Divide mixture in 1/2 and place between cellophane. Shape with fingers and spread to the same length and width of the lamb loin.
Roll the tenderloin in the mushroom powder (this will provide a visual break between the loin and the tenderloin in the completed dish as well as enhance the flavor.)
Position each loin halfway on top of each of the ground lamb mix and place the tenderloin on top of the loin. Lift the cellophane and contour the meat around the tenderloin and press against the loin. Wrap with a single layer of caul fat and tie with butcher's twine at 1-inch intervals.
Preheat the oven to 375 degrees F.
In a large ovenproof saute pan over high heat add vegetable oil, season meat and sear in pan until all sides are nicely browned. Place pan in the oven and continue to cook approximately 15 minutes until the desired temperature is reached.
Remove meat from pan and allow to rest 10 minutes before slicing (twine can be removed.)
Deglaze the pan with lamb stock, reduce to a sauce consistency and adjust seasoning.
Serve on warm serving plates with potatoes, spinach and thick slices of the lamb. Spoon sauce over the top and serve.
In a large pot of boiling, salted water, quickly blanch the spinach and refresh in ice water. Allow spinach to completely cool, then, using a clean dish towel wring out all of the excess water and finely chop.
In a large sauce pot over medium heat place the cream. Bring the cream to a simmer and allow to reduce by 2/3, add nutmeg and season, to taste. Hold warm. Just before serving, add the spinach and mix well.
Slice potatoes 1/4-inch thick and using a cookie cutter, punch out disks of the potato and place in cold water (reserve the trim for another use).
In a large saute pan over high heat, place duck fat and then add the potatoes (which have been drained and patted dry.) Cook potatoes until they have a tender interior and a golden exterior.
Season and hold warm.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.