Follow package instructions for the macaroni, but cook to a very firm texture. Don't let it get soft. It should seem almost undercooked. The macaroni will soften up more later on when its combined with all of the other ingredients and baked. Once the macaroni is cooked, drain and set aside.

Preheat oven to 350°.

Using a large pot, melt butter over medium low heat and add the flour. Whisk constantly for approximately 6 minutes. The butter and the flour should be integrated and slightly bubbly. Watch the temperature to avoid burning. 

Add the milk and mustard, whisking to a smooth consistency. Whisk regularly for approximately 8 minutes, until thick. Reduce heat to low. 

Temper the eggs. To do this, scoop out 1/2 cup of the butter/flour/milk mixture from the pot, and slowly pour it into the beaten eggs in a separate bowl, all while whisking constantly. 

Now add the egg mixture back into the sauce in the larger pot. Whisk constantly until smooth and integrated. 

Add the cheeses and stir to melt and integrate. 

Add in the salt and seasonings. 

Add in the cooked macaroni and stir until all macaroni is coated with the sauce. 

Pour into two, buttered 9x13 rectangular baking pans or one large 10x13 deep dish baking pan. Sprinkle tops with 2 tbsp of shredded cheese. Bake for 25 minutes until golden and bubbly.