Boil elbows in generously seasoned water with Pro Boil seasoning. Cook them about 2 minutes shy of done. Drain.
While they're hot, toss the elbows with 2–3 tablespoons butter.
Mix in the tuna, cream of mushroom soup, cheddar, about ½ cup milk, a little more Pro Boil and black pepper. Add another splash of milk if it looks too thick.
Spread into a greased casserole dish.
Cover the top generously with Mexican blend cheese. Add buttery Ritz crumbs if you want the classic crunchy top.
Bake 20–25 minutes, until bubbling around the edges. Broil for 1–2 minutes at the end if you want the cheese browned.
One thing I'd add: a little onion. Either ½ small onion sautéed in the butter or about ½ teaspoon onion powder. It gives that traditional tuna-casserole flavor without turning it into something fancy.
And don't overcook those elbows before baking — that's the difference between creamy casserole and tuna-flavored mush.