Mini Wellingtons (Individual Serving)
- Peel shallots, cut in half lengthwise, then cut crosswise into 1/2-inch-thick slices. Melt butter with 1 1/2 tablespoons oil in a large, heavy frying pan over medium heat. Add shallots; reduce the heat to medium-low. Cook, stirring frequently, until shallots are nicely browned, translucent and tender, about 12 minutes. Remove from heat.
- Sprinkle one side of each steak with salt and pepper to taste. Place a heavy medium frying pan over high heat for 3 to 4 minutes, until pan is very hot. Add the remaining 2 tablespoons oil, then sear the steaks for 1 minute per side. Transfer steaks to a dinner plate; let cool for 5 minutes. Top each cooled steak with a generous teaspoon of mustard, one-quarter of the shallots and 1 tablespoon cheese.
- On a floured work surface, roll puff pastry into a 12-inch square. Cut pastry into four 6-inch squares. Brush a 1/2-inch border around each square with beaten egg. Refrigerate the remaining egg.
- Place a pastry square (brushed-side down) over a steak; carefully lift the meat and press the pastry around its sides, then seal tightly on the bottom. Place on a (foil lined) lightly oiled baking sheet. Repeat with the remaining sheets. Refrigerate the Mini Wellingtons for 45 to 60 minutes.
- Preheat the oven to 425 degrees. Brush the tops and sides of the pastry enclosing each steak with some of the reserved beaten egg. Sprinkle the tops with a pinch of fleur de sel.
- Roast on the middle oven rack until the pastry is golden brown and a thermometer inserted through the pastry to the center of the meat registers 135 degrees to 140 degrees for medium-rare, 15 to 18 minutes.
- Transfer the Mini Wellingtons to a rack and let rest for 5 minutes before serving.