Preheat oven to 375ºF.
Rub and season both sides of beef medallions with 1 tbsp of the oil, salt and pepper.
Heat 1 Tbsp butter with remaining oil in a heavy skillet over medium-high heat; brown meat on both sides, about 1 to 2 minutes per side. Transfer to a baking sheet.
In same skillet, melt remaining butter; add shallots and onion and cook over medium-high heat, stirring, until softened for about 1 minute. Add mushrooms and cook, stirring occasionally, until there is no liquid from the mushrooms remaining, about 5 to 10 minutes. Season to taste. Set aside to use for Madeira Mushroom Sauce.
Top each medallion with paté slices and mushroom mixture. Bake in oven for 8 to10 minutes to finish. Serve with Madeira Mushroom Sauce and 1 to 2 Wellies.