Preheat oven to 375 F.

In a large pot (8 qt), boil pasta about 3 minutes under package time so it still has bite - it will finish cooking in the oven. Reserve about 1 cup pasta water, then drain.

Set the empty pasta pot back on the stove over medium heat and melt the butter.

Add the flour and dry seasonings, mix well and stir continuously for a couple minutes to cook out the flour taste. The roux should be a light golden brown.

Reduce heat to medium-low and slowly stream in the half and half and milk while whisking continuously. Don't stop whisking.

While whisking the milk mixture over medium-low heat, add the velveeta cubes and whisk until melted and combined.

While still whisking constantly, add 2 cups of the cheddar and 2 cups of the gruyere in handfuls, whisking each handful in thoroughly before adding the next.

Once all 4 cups of shredded cheese have melted and combined into the sauce, remove the pot from the heat.

Add in the reserved pasta water, about 1/4 cup at a time, until a velvety, pourable, heavy cream consistency has been reached.

Dump the cooked and drained pasta into the pot and mix the sauce and pasta together thoroughly.

Lightly grease a 9x13 baking dish and pour half of the pasta mixture into the bottom, spread evenly.

Layer 1 cup of the remaining shredded cheddar.

Pour the rest of the pasta mixture and spread it evenly.

Add a top layer of the remaining cheddar and shredded gruyere.

Bake uncovered for 10-15 minutes or until the top layer of cheese is melted and bubbly.

Remove from oven and let cool for about 5 minutes.