Preheat the oven to 350 degrees F. Butter a 2-quart baking dish or 10” cast iron skillet with 1 tablespoon of the butter and set aside. We like to cook our mac in cheese in our 10” cast iron skillet.
Bring a large pot of salted water to a boil. Add the macaroni and cook until al dente, about 10 minutes. Drain in a colander and rinse under cold running water. Drain well.
Melt the remaining 6 tablespoons butter in a heavy 3-quart saucepan over medium heat.
Add the flour, and stirring constantly with a wooden spoon, cook over medium heat for 3 to 4 minutes, being careful not to let the flour brown.
Using a whisk, add the milk in a steady stream and cook, whisking constantly, until thick and smooth, 4 minutes.
Remove from the heat. Add the salt, pepper, and 2 cups of the cheese, and stir well.
Add the noodles and the brisket and stir well. Pour into the prepared skillet.
Mix the remaining ½ cup of cheese, the bread crumbs and the grill seasoning together in a small bowl and sprinkle evenly over the macaroni and bake until golden brown and bubbly, about 25 minutes.
Remove from the oven and let rest for 5 minutes before serving.