Start by preheating your oven to 350 degrees F. Cook your choice of pasta in boiling salted water until it’s just al dente, usually a minute less than the package suggests.
Turn the heat to low and start adding the cheeses (save 1/2 cup of cheddar for later). Add them slowly, one handful at a time, stirring until each batch is melted before adding more.
Combine the cooked pasta and crabmeat in a 9×13 inch baking dish or a 5-quart pot. Pour the cheese sauce over and stir to mix everything well. Sprinkle the top with the reserved cheddar.