Crush the ranch Doritos into crumbs.
Preheat the oven to 350 degrees.
Cook the ground beef and onions in a skillet over medium high heat until the meat is browned and the onions have softened.
Reduce the heat to medium.
Stir in the garlic, and saute 30 seconds.
Mix in the taco seasoning, ranch seasoning, corn and tomatoes. Simmer for a minute or two.
Stir in the sour cream and 1 ½ cups of the taco blend cheese until melted and combined.
Add in 2 cups of the Dorito crumbs and stir.
Spread the mixture into a well greased 9x13 baking dish.
Bake for 10 minutes.
Remove, add the remaining cheese and Dorito crumbs, and bake for another 5 minutes.