Melt the butter in a large saucepan.

Add the diced onions and cook until they are tender and translucent.

Add the squash, chicken stock, salt and pepper to taste and bring to a boil.

Reduce the heat and simmer for 20 minutes until the squash is tender.

Using an immersion blender, puree the mixture until smooth.

Stir in the heavy cream and season with tarragon.

Add additional salt and pepper as needed.