Spread a little 6-ingredient happiness, also known as cheese sauce, across your Tex-Mex casserole for an extra cheesy bite.
Melt butter in heavy saucepan over medium-low; whisk in flour until smooth. Cook, whisking constantly, 1 minute. Increase heat to medium. Gradually whisk in milk; cook, whisking constantly, until thickened, 5 minutes. Remove from heat, and whisk in cheese, chiles, and salt. Use immediately.