Remove the phyllo shells from the freezer and place them on the kitchen counter. Allow them to come to room temperature. 

Next, preheat a large non-stick skillet to medium-high heat. Add the olive oil, American lamb leg roast cubes, kosher salt and pepper. Sear the cubes, about 2 minutes per side until golden brown. Remove the cubes from the skillet with a slotted spoon and set aside on a plate to rest for at least 3 minutes. 

In the same skillet as the lamb, add the white wine and deglaze the skillet over medium-high heat. You want to scrape up any browned bits from the bottom! Next, melt the butter and add in the mushrooms and cook until softened, about four to 5 minutes. Next, add in the shallots, garlic, rosemary, kosher salt and pepper. Stir and keep cooking for about 5 more minutes. 

Next, add in the flour and cream.Stir to combine and cook for about a minute. Add in the reserved lamb cubes and heat through. Remove skillet from heat. 

To serve, place mini filo shells on a serving platter. Spoon the lamb wellington mixture into each filo shell and garnish with chives. Serve and enjoy!