In a heavy saucepan, melt butter over medium-low heat. Whisk in flour until smooth; cook for 1 minute, whisking constantly. Gradually whisk in milk; increase heat to medium, and cook, whisking constantly, until thickened, about 5 minutes. Remove from heat, and whisk in cheese, green chiles, and salt.
Recipe by Southern Cast Iron at https://www.southerncastiron.com/breakfast-enchiladas/