Place cubed butternut in a heavy-bottomed pot, add salt and about 2 cups of water,( butternut contains a lot of water), cover and cook until tender enough to mash. Drain and mash.
In a separate skillet on medium-high heat, add butter and melt. Add the brown sugar and cook until completely dissolved, add cinnamon. Add caramel mixture to mash butternut squash and stir until thoroughly mixed.