Cook the noodles to al dente. Do not overcook. Drain once cooked and set aside.
For the breadcrumbs, toast the bread and finely chop into crumbs; a food processor works well here.
Melt the butter over medium heat. Stir in the garlic.
Whisk in the flour, which will form a thick paste. Season with salt and pepper.
Stir in the pumpkin, rosemary, and cayenne.
Whisk in the milk, adding slowly as if you are making gravy.
Stir in 3/4 of the cheese. Once mostly melted, turn off the heat.
Stir in the noodles. Top with the remaining cheese and then the breadcrumbs and remaining rosemary.
Cover and bake at 350°F for 15 minutes. Remove cover and bake an additional 15 minutes.
Notes
You can use other noodles besides macaroni, like shells or bowtie. But I would stick with noodles that have a similar shape/density. So, avoid things like spaghetti as this will make serving a little harder (not as easy to spoon out of the pan).Wheat bread is preferred for the breadcrumbs, but you can use any old bread you may have on hand. I just like the hardiness of wheat.