You could also substitute butternut squash for pumpkin.
The acidity from the tomato paste cuts the natural sweetness of the pumpkin.
Our family is crazy about Dubliner cheese. It has a nutty flavor with a mild fruitiness. If you don't find it, you can replace it with another aged cheese such as Parmesan.
To make béchamel sauce, always make sure all the ingredients are at the same temperature, so heat the milk in the microwave for about 2 minutes (or in a saucepan), so it's warm. If you get lumpy pieces in the sauce, don't hesitate to use a hand blender.
And if you're a pasta lover, check out my other pasta dishes.