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.