In a heavy bottomed dutch oven (big enough to hold all the pasta) set over medium high heat, add the pumpkin and cook – continuously stirring – until some of the moisture has evaporated. Add the butter and stir until melted and completely combined with the pumpkin.
Sprinkle the flour over the mixture and whisk to combine, cooking for about one minute. While continuing to whisk, add the cream, creating a smooth sauce. Add the cheese in small handfuls, stirring until melted. Add the pasta and gently toss to coat in the cheese and pumpkin sauce. Turn off the heat. Add more cream or half and half if the pasta soaks up too much of the sauce and seems too dry.
Evenly sprinkle the bread crumbs, pepitas, and sesame seeds over the top of the pasta. Place under a high broiler until the bread crumbs just begin to brown – moving the dutch oven around as necessary. Serve hot.