Preheat oven to 300 degrees F.
Add oil to saute pan. Season meat on all sides with salt and pepper. Sear meat on all sides, about 2 to 3 minutes each side. Place meat on sheet tray with a rack. Roast meat for 30 to 40 minutes. Crank oven up to 450 degrees F. and roast for an additional 15 to 20 minutes until crust forms and meat is nicely colored. When done, allow to rest before slicing. In a small bowl reserve juice for Bourbon Mushroom Sauce.
In a large saucepan over medium-high heat, add 4 tablespoons butter. Add garlic, mushrooms and onion and cook for 4 to 5 minutes until nicely Add flour and mix well to form pasty roux.
When adding alcohol to any dish, remove pan from flame. Add bourbon and scrape pan with a wooden spoon. Add stock and mix well removing any lumps. Bring sauce to a boil and allow to simmer for 10 minutes until sauce thickens. Add salt and pepper, if needed. Add 1 tablespoon cold butter and whisk together. Stir in reserved roast beef juice. Finish with parsley. Serve on top or along side of roasted meat.
Use extreme caution when igniting alcohol. Remove the pan from the heat source before adding the alcohol. Pour the alcohol into the pan and carefully ignite with a match or click lighter. Return the pan to the heat and gently swirl to reduce the flames.