Cook pasta in boiling salted water until al dente. Rinse and set aside.
In a large saunce pan over medium high heat, melt the butter. Add the flour and whisk with butter until golden brown. Add 1 cup of milk and rosemary and whisk until smooth. Add another cup of milk and stir constantly until thick and bubbly. (This will take a few minutes.)
Add all but a small handful of the grated cheese to the sauce and stir until melted. Stir in the pumpkin puree and paprika- add salt & pepper to taste.
Add the cooked pasta and toss to coat. Pour into a 9x13 casserole pan and top with the panko and remaining cheese
Bake for 20-25 minutes until golden brown and bubbling. Let cool slightly before serving.