Bring a large pot of salted water to a boil and cook noodles until they are al dente.
Shred the block of white cheddar cheese.
In a medium pot, combine milk and half and half and gently warm but do not let boil. In a separate large pot, melt butter over med-low heat. Whisk in flour until smooth and thick. Slowly add warm milk into flour mixture, whisking to smooth out any chunks. Add mustard, nutmeg, salt and pepper. Slowly add cheddar, whisking in until the cheese begins to melt. Add swiss/gruyere mix and continue whisking until semi-smooth (you will have some globs of cheese).
Pour noodles into a 13×9 baking pan. Pour cheese mixture over noodles, sprinkle with more salt and pepper and mix well. Using a kitchen shears, snip rosemary sprigs into small pieces over the macaroni. Use your fingers to strip any remaining leaves off the rosemary. Stir again and sprinkle panko crumbs over the entire dish. Bake for 40-45 minutes.