Cut the crown prince pumpkin into wedges. Coat with olive oil and season with kala namak.
Roast in the oven for 20, flipping over halfway to get a nice colour on both sides.
While the pumpkin is roasting, peel and slice the onions. Wash and slice the ginger.
In a pot, add the onion, ginger, sake and rice vinegar and bring to a rapid boil. Then immediately reduce the heat to simmer. Simmer until the liquid has reduced in half. Pass the reduction through a sieve. Discard the onion ginger.
Melt the vegan block butter and set aside.
Once the pumpkin is cooked, peel the skin and add wedges to a blender along with the sake-vinegar reduction and blend to a smooth puree. Adjust the seasoning if required.
While continuing to puree, add the melted butter and continue to blend until the butter is incorporated and you have a smooth puree.
Garnish with roasted pumpkin and sesame seeds, and serve warm with crackers.