Mushroom Soup
1/2 lb. mushrooms 4 cups White Stock III 1/4 cup pearl sago 1 cup boiling water 1 cup heavy cream Yolks 2 eggs Salt and pepper Clean and chop mushrooms, and add to stock. Cook twenty minutes and rub through a sieve. Cook sago in boiling water thirty minutes, add to stock, and as soon as boiling-point is reached, season with salt and pepper; then add cream and yolks of eggs.
A cream soup thickened three ways at once — sago, cream and egg yolks — which is what makes the last step the one that matters.
- Do not boil after the yolks go inBring the soup to the boiling point before adding cream and yolks, then keep it below a simmer. Temper the yolks with a ladle of hot soup first, return them to the pan, and hold it around 175F until slightly thickened; a boil will curdle it into threads.
- White Stock IIIFarmer's white stocks are mild, unbrowned broths built on veal and/or fowl, with seasoning generally added later rather than in the stockpot. A light chicken stock or a veal stock stands in; avoid anything dark or heavily seasoned, since the point is a pale soup.
- Pearl sagoSago is palm-starch pearls, still sold in Asian and Indian groceries. Small pearl tapioca is the closest substitute in the same quantity. Thirty minutes in a cup of boiling water is right for old-style sago; modern quick-cooking pearls soften in ten to fifteen, so check rather than time.
- MushroomsHalf a pound of ordinary cultivated white or cremini mushrooms works. Period cookbooks often directed peeling mushrooms and trimming the stems; there is no need to peel today, but wipe rather than soak them.
- "Rub through a sieve"A blender or immersion blender does this in seconds; pass it through a fine strainer afterward if you want the smooth texture the sieve gave. Expect the soup to be pale grey-brown rather than white.
- CreamA cup of heavy cream to four cups of stock is rich by current standards. Half the amount, or half-and-half, gives a soup that tastes more of mushroom and less of dairy.
- SeasoningAn unsalted white stock means all the salt comes at the end. Season after the sago goes in and before the enrichment, then taste again once the cream is in — fat blunts salt.
- YieldAbout five cups finished, serving four generously or six as a first course. It does not reheat well: warm gently, never to a boil.
Mushroom soup thickened with sago sits at the point where two nineteenth-century habits met. Cream soups bound with egg yolk and cream come from the French velout ies schools taught as a matter of course, while sago he ssago palm, imported through the East Indies trade y and puddings, valued because it thickened without flour and was considered easy to digest. Farmer's soup chapter is organised as a teaching sequence, with numbered stocks referred to across other recipes, so a reader was expected to have made White Stock III already. Cultivated mushrooms were still a relative novelty in American markets at the time; commercial growing in the United States is generally traced to the last decades of the nineteenth century, which is part of why a half-pound of them reads here as a small, carefully stretched luxury.