Preheat the oven to 400 degrees.
In a large pot of boiling water, cook the pasta according to package instructions until just al dente.
Pour into a colander, rinse with cold water, and drain well. Set aside.
In a large, heavy-bottomed saucepan, melt the butter over medium heat.
Whisk in the flour, and cook until the mixture is bubbling and takes on a golden tan color, about 2 minutes.
Slowly whisk in the warm milk, and cook until bubbling and begins to thicken, about 10 minutes.
Remove from the heat, and whisk in the Cheddar, Gruyère, and Parmesan.
Season with salt, pepper, lemon zest, and cayenne, stirring until incorporated. Taste and adjust seasoning, if desired.
Fold the drained pasta into the sauce, followed by the crab meat.
Pour the mixture into a shallow 2-quart baking dish that’s been greased with a little butter.