Creamed Chipped Beef

Ingredients

• 3 tablespoons unsalted butter, plus more if needed
• Two 8-ounce top sirloin steaks
• Kosher salt and freshly ground black pepper
• 1 1/2 cups sliced cremini mushrooms
• 1/2 cup diced yellow onion
• 3 cloves garlic, chopped
• 2 tablespoons all-purpose flour
• 1 teaspoon English mustard, such as Coleman's
• 1 cup milk
• 2/3 cup chicken broth
• 1/2 cup stout beer or Madeira wine
• 1 tablespoon Worcestershire sauce
• 2 tablespoons chopped fresh parsley, plus more for garnish
• 4 slices thick-cut country bread