Beef Tenderloin Sandwich w/ Norton-Shiitake Sauce

1. In a large, deep skillet, melt 4 tablespoons of the butter. Add one-third of the minced garlic and all of the scallions and cook over moderately high heat for 1 minute. Add the shiitakes and cook until slightly softened, about 2 minutes. Add the chili powder, thyme and 1 teaspoon of pepper and cook over moderate heat, stirring occasionally, until the shiitakes begin to brown, about 5 minutes. Add the stock, wine and soy sauce and bring to a boil. Simmer gently until reduced to 1 cup, about 40 minutes. Stir the cornstarch slurry and whisk into the liquid. Cook, stirring, until slightly thickened, about 2 minutes. Season with salt; keep warm.
    
2. Preheat the broiler. Cut the baguettes into thirds and split the pieces lengthwise, taking care not to cut all the way through. In a small saucepan, melt the remaining 4 tablespoons of butter. Add the remaining minced garlic and cook over low heat until fragrant, about 4 minutes. Brush the garlic butter on the baguettes and sprinkle lightly with salt. Broil the bread, cut side up, for about 1 minute, until golden.
    
3. Preheat a grill pan. Brush the tenderloin slices with oil; season with salt and pepper. Grill the meat in batches over high heat, turning once, until charred and medium-rare, about 5 minutes. Dip the meat in the mushroom sauce and arrange on the baguettes. Spoon the mushroom sauce on top, close the sandwiches and serve.
    
4. Serve with Yukon Golds with Shallot Butter

*recipe from foodandwine.com