Using a sharp knife, slice the bottom and top off the celeriac bulb. Switching to a smaller knife if necessary, slice the skin off the bulb, as if you were making citrus suprȇmes. Do not worry about removing too much flesh; it is somewhat impossible to avoid.

Melt the butter in a large, heavy-bottomed saucepan. While the butter is melting, cut the celeriac into medium chunks.

Add the shallot to the melted butter and cook for 2 minutes. Then add the celeriac, stir to coat, and season with kosher salt. Sauté until the chunks of celeriac become browned and begin to soften.

Add the stock, and bring to a simmer. Continue to simmer, for 30 minutes or so, until the celeriac chunks are cooked through and the stock has reduced (it should just cover the vegetables).

Transfer to a high-powered blender, such as a Vitamix, and purée until completely smooth. Return to the saucepan and whisk in the cream. Simmer gently for 10 minutes or so, allowing the flavors to meld.

Taste the soup and correct the seasoning. Divide among serving bowls, and garnish with chives if desired.