Mix the milk with the cornstarch and whisk until smooth.
Cook the milk in a small frying pan over medium heat, whisking constantly, until it just comes to a simmer and thickens up. Remove from heat.
Stir in the cheese until melted, turning the heat on slightly once or twice if needed, but being careful not to overheat cause it could separate.
Stir in the creole seasoning. Set aside - I like to put it in a thermos to stay hot until ready to use. If it feels too thick you can add a splash of milk.
Cook the andouille in a pot on high heat with a little oil to brown on all sides. Remove from the pot with a slotted spoon, keeping the oil in the pot.
Add the shrimp and cook about 3 minutes per side until cooked through. Remove with a slotted spoon.
Add in the contents of the rice packet along with 2 1/4 cups of water. Stir to combine and bring to a simmer. Turn the heat to low and cover, until the water is absorbed and the rice is tender.
Build the nachos starting with the rice, then the sausage and shrimp, and finish with the cheese sauce. Serve.