1. Preheat oven to 475ºF. Take 1 T. of butter and thickly grease an 11×17 inch jelly roll pan. Make sure every inch is covered.
2. In a large heatproof bowl combine the cheese and set aside 2 c. in a separate measuring cup.
3. Bring a large pot of salted water to a boil, add the pasta and cook for 6 minutes. Drain.
4. Working quickly, put the drained pasta in the bowl with the cheese, add the mustard, a pinch of salt, the bacon pieces and panko. Using a wooden spoon, toss the mixture until all evenly incorporated.
5. Next, spread the mixture onto the buttered sheet pan and pour the milk evenly over the surface. Top with the remaining cheese and dot with remaining butter.
6. Finally, bake it for 15 minutes, until golden and crisp.