Crumble chorizo into a large skillet; cook over medium heat for 6-8 minutes or fully cooked. Drain.
In a large bowl, whisk the eggs, milk, mustard and cayenne. Stir in the potatoes, cheese, salsa, and cooked chorizo. Transfer to a greased 9x13 inch baking dish. Cover and refrigerate overnight.
Remove from the refrigerator 30 minutes before baking. Bake, uncovered, at 350°F for 55-65 minutes or until a knife inserted near center comes out clean.
Let stand 10 minutes before cutting.