Preparation Melt 1 tablespoon butter in medium skillet over medium-high heat. Sprinkle steaks with salt and pepper. Add steaks to skillet and cook until medium-rare, about 4 minutes per side. Transfer steaks to plate. Cut steaks into 1/2-inch cubes. Melt remaining 2 tablespoons butter in same skillet. Add potatoes, leeks, and dry mustard. Stir 1 minute. Reduce heat to medium, cover, and cook until potatoes are tender, stirring occasionally, about 8 minutes. Return beef and any accumulated juices to skillet. Add steak sauce and sauté 2 minutes. Remove skillet from heat. Mix in green onions. Season filling to taste with salt and pepper. Cool completely. Preheat oven to 400°F. Unfold crusts on work surface. Cut each crust into 2 pieces along center fold. Brush dough with egg. Place 1/2 cup filling on half of each piece. Fold plain dough over filling; seal edges. Brush pies with more egg; arrange on 2 baking sheets. Bake pies 15 minutes. Reverse sheets. Bake until crust is golden and filling is heated through, about 10 minutes.
Preparation Melt 1 tablespoon butter in medium skillet over medium-high heat. Sprinkle steaks with salt and pepper. Add steaks to skillet and cook until medium-rare, about 4 minutes per side. Transfer steaks to plate. Cut steaks into 1/2-inch cubes. Melt remaining 2 tablespoons butter in same skillet. Add potatoes, leeks, and dry mustard. Stir 1 minute. Reduce heat to medium, cover, and cook until potatoes are tender, stirring occasionally, about 8 minutes. Return beef and any accumulated juices to skillet. Add steak sauce and sauté 2 minutes. Remove skillet from heat. Mix in green onions. Season filling to taste with salt and pepper. Cool completely. Preheat oven to 400°F. Unfold crusts on work surface. Cut each crust into 2 pieces along center fold. Brush dough with egg. Place 1/2 cup filling on half of each piece. Fold plain dough over filling; seal edges. Brush pies with more egg; arrange on 2 baking sheets. Bake pies 15 minutes. Reverse sheets. Bake until crust is golden and filling is heated through, about 10 minutes.