Roast Beef Hash

Ingredients

• 3 tablespoons unsalted butter
• 1 medium onion, chopped
• 1 pound mashing potatoes, cooked, peeled, cooled and cut into 3/4-inch cubes
• 2 pounds rare-cooked roast beef, cut into 3/4-inch cubes
• 1 cup beef stock
• 6 ounces fresh spinach leaves, blanched and squeezed dry
• 1/4 cup chopped fresh parsley
• 1/2 teaspoon fresh thyme, chopped, or a pinch of dried
• 1/2 teaspoon fresh sage, chopped, or a pinch of dried
• Salt and freshly ground black pepper