Wash the potatoes and pumpkin. Remove the seeds from the pumpkin and cut the pulp into wedges. Halve the potatoes. Line a baking sheet with parchment paper and brush it with the olive oil. Put the potatoes and pumpkin on top. Chop the sage and season the vegetables with the chilli flakes, pepper and sea salt. Put the tray in the oven for 30 minutes to soften the vegetables.
Then hollow out the potatoes and place the inside (without the skin) in a shallow bowl. I always leave the skin on with Hokkaido, if you don`t want to have it in the puree afterwards, you should also remove the skin from the pumpkin. Then add the pumpkin meat to the bowl as well. Roughly mash with a pounder. Mash or stir by adding milk and butter to an even, creamy puree. If necessary, season with salt.