Boil about 2 quarts of salted water in a pot, and cook the macaroni for 4 minutes. Add the frozen broccoli and cook for another 5 minutes.
If you're like me and get absentminded of what's in your freezer and how long it's been in there thus your broccoli is REALLY freezer-burnt, throw it in the pot when you put the macaroni inches Make sure it's a big enough pot.
When they're all done cooking, remove and drain the macaroni and broccoli. Put them into a 2.5-quart baking dish, mixing well.
Pour the milk into the pot and let it come to a low boil. Meanwhile, preheat the oven to 350°F.
While waiting for the milk to heat up, combine the sour cream, tablespoon of milk, flour, and spices in another bowl to make a paste.
Add this paste to the boiled milk, and stir thoroughly.
When the mixture becomes thick, add 3/4 cup of cheese and it should melt on impact. Stir again to fully incorporate the cheese.
Pour the cheese sauce over the macaroni and broccoli, blending well. Top evenly with the 1 1/4 cups cheese.
For the panko topping, melt the butter in a frying pan or saucepan and toss with the panko flakes until nice and toasty. Put over the cheese.