Preheat Oven: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish with non-stick spray or olive oil.
Prepare the Filling: In a large frying pan, heat the Potatoes O’Brien over medium heat until golden and heated through. In a separate large bowl, whisk together eggs, half-and-half, flour, and kosher salt. Cook the egg mixture gently in the frying pan over low heat until just set. Combine the cooked potatoes, eggs, ¾ cup cheddar cheese, ¼ cup Monterey Jack cheese, and salsa in a medium mixing bowl. Stir until evenly distributed.
Assemble the Enchiladas: Lay a tortilla flat and spoon about ⅛ of the filling into the center. Roll tightly and place seam-side down in the prepared baking dish. Repeat with the remaining tortillas and filling.
Add Topping: Pour the remaining egg mixture over the rolled tortillas. Sprinkle the top with the remaining cheddar and Monterey Jack cheese.
Bake: Cover the dish with foil and bake for 35 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Serve: Allow the enchiladas to cool for 5 minutes before serving. Garnish with optional toppings like cilantro, tomatoes, or green onions for added flavor and freshness.