Cut the beef with the grain into 2½- to 3-inch-wide strips and place them on a large plate. Freeze until firm, about 15 minutes. Then, slice the strips crosswise against the grain into ⅛-inch-thick pieces. Toss the beef with cornstarch in a bowl and set aside.

Set a wire rack in a rimmed baking sheet. Heat oil in a large Dutch oven over medium-high heat until it reaches 375°F. Add one-third of the beef and fry, stirring occasionally, until browned and crispy, about 4 minutes. Adjust the heat as needed to keep the oil temperature between 350°F and 375°F. Transfer the beef to the prepared rack using a slotted spoon or spider skimmer. Return the oil to 375°F and repeat with the remaining beef in two more batches.

Transfer 1 tablespoon of the frying oil to a 12-inch nonstick skillet and heat over medium-high until shimmering. Add the scallion whites, arbol chiles, garlic, and ginger, cooking until fragrant, about 30 seconds. Stir in the water, sugar, and soy sauce, bringing to a vigorous simmer. Cook until the sauce thickens and reduces to about 1¼ cups, 6 to 8 minutes.

Add the fried beef and scallion greens to the sauce, tossing constantly until the beef is well coated, about 1 minute. Transfer to a platter and serve with rice.