Transform leftover roast beef hash recipe into a hearty, crispy hash. Dice cooked roast beef, potatoes, and onions into small, even pieces. Heat butter or oil in a skillet over medium-high heat, then sauté the onions until soft. Add the potatoes and cook until golden and lightly crisp. Stir in the roast beef, seasoning with salt, pepper, and a pinch of paprika. Press the mixture down to form a crust, letting it brown before flipping. Cook until everything is crisp and caramelized. Serve hot with fried eggs on top for a comforting, flavorful breakfast or quick dinner.