Pour the quart of whole milk into a small saucepan and heat on medium heat until it coats the back of a wooden or cooking spoon. Turn off heat before it starts to boil; set aside for later.
Grate cheeses (8 oz. white cheddar and 3/4 cup freshly grated parmesan) and set aside. Cook elbow pasta in stockpot according to package directions. Drain and set aside.
Preheat oven to 400 degrees.
Add 1/2 cup of butter to the now empty stockpot you used to cook the pasta. Cook on medium heat until melted.
Whisk 1/2 cup of flour into the butter and allow to cook for 2-3 minutes until lightly browned and bubbling.
Slowly add warm milk to the butter/flour mixture, whisking with each addition until smooth. Stir in kosher salt.
Cook on medium heat for five minutes or until slightly bubbling. Add cheeses and stir until melted. Once melted, turn off heat.
Add cooked pasta to the cheese sauce and mix thoroughly. Pour into 9x13 casserole dish. Top with one cup of panko breadcrumbs.
Bake for 20 minutes or until bubbling. Remove from oven and serve hot.