Brown the chorizo, onion, and jalapeño until chorizo is fully cooked and the vegetables have softened.
Spread the mozzarella evenly over the chorizo.
Sprinkle the fresh cilantro over the top as a garnish flourish.
Bake for 15-20 minutes.
Serve hot and enjoy.
Notes
Use Fresh Mexican Chorizo: This is the most important tip. You want fresh, uncooked Mexican chorizo, not the hard, cured Spanish variety. Mexican chorizo is sold in casings or as loose ground meat. Remove the casings before cooking and crumble it as it browns.Don't Skip Draining the Grease: Chorizo can render a lot of fat as it cooks. While a little grease adds flavor, too much will make the dip oily. After browning, tilt the skillet and spoon off the excess grease, leaving just enough to coat the bottom.Shred Your Own Cheese: Pre-shredded mozzarella contains anti-caking agents like cellulose that prevent it from melting as smoothly. For the best bubbly, stretchy cheese top, buy a block of mozzarella and shred it yourself.Use a Hot Skillet Handle Cover: Cast iron handles get extremely hot in the oven. Always use a silicone handle cover or a thick towel when removing the skillet, and leave the cover on while the dip is on the table so no one accidentally grabs a 350°F handle.Serve It Fast: This dip is best served immediately while the cheese is still hot and gooey. Once it cools, the cheese firms up. If you need to keep it warm for a party, place the skillet on a trivet over a warming tray, or transfer the dip to a small slow cooker on the "warm" setting.