01 -
Preheat oven to 400°F/206°C. Cook spaghetti in boiling water for 6 minutes. It should be slightly underdone as it will continue cooking in the oven.
02 -
Melt butter in a medium pot over medium heat. Add flour and whisk together for 30 seconds to create a roux. Add kosher salt, black pepper, cayenne, and granulated garlic and mix well.
03 -
Gradually whisk in the half and half in thirds to prevent lumps, then add the heavy cream. Bring the mixture to a boil. Once boiling, add 2 cups of sharp cheddar and 1 cup of mozzarella. Reduce heat to medium-low and stir until the cheese has completely melted and the sauce is smooth.
04 -
Add the cooked spaghetti to a 9x13 casserole dish. Sprinkle 1 cup of mozzarella and 1 cup of cheddar over the pasta. Pour the cheese sauce over everything and stir to combine. Sprinkle the remaining 2 cups of cheddar and 2 cups of mozzarella over the top.
05 -
Bake in the preheated oven for 25 to 30 minutes, until the cheese on top has melted and browned evenly. For even browning, rotate the pan halfway through baking.
06 -
Remove from the oven and let stand for 5 minutes. Cut into squares and serve immediately while hot and bubbly.