In a shallow bowl, whisk the flour, salt, pepper, garlic powder, and onion powder.
⅓ cup all-purpose flour, ½ teaspoon kosher salt, ¼ teaspoon ground black pepper, ½ teaspoon garlic powder, ½ teaspoon onion powder
Dredge the steaks in the flour mixture, shaking off any excess.
4 cube steaks
Heat the oil and butter in a large skillet over medium heat until melted. Add in the steaks and cook for 3-4 minutes per side. Remove from the pan and set aside.
1 tablespoon vegetable oil, 1 tablespoon unsalted butter
To the same pan, melt the remaining butter. Add in the onions and cook, stirring often, over medium heat until softened and beginning to carmelize, about 10-12 minutes.
2 tablespoons unsalted butter, 1 yellow onion
Stir in the garlic and rosemary. Cook, stirring until fragrant, about 60 seconds.
1 tablespoon minced fresh rosemary, 3 cloves garlic
Stir in the beef broth and sherry vinegar. Bring to a simmer and cook, stirring occasionally, until the sauce has reduced slightly, 5-7 minutes. Taste and season with salt and pepper to taste.
1 cup low-sodium beef broth, 1-2 tablespoons sherry vinegar, Kosher salt and freshly ground black pepper
If you would like the gravy to thicken further, remove the pan from the what and whisk in the cornstarch and water mixture. Return to the heat and stir constantly until the sauce simmers.
1 teaspoon cornstarch
Return the steak to the pan. Spoon the gravy over the steaks.