Creamed Mushroom Toast

A short, rich creamed-mushroom sauce spooned over toast — the kind of light supper or breakfast dish that filled the savoury pages of turn-of-the-century compilations. The instructions assume a cook who knows when to stop reducing.

• The hinge: the egg yolkIf you use the yolk to thicken, take the pan off the heat, whisk a little of the hot cream into the beaten yolk, then return it and hold the mixture below a simmer. Boiling after the yolk goes in curdles it into grains.
• No mushroom quantity is givenThe original leaves the amount to the cook. For 1/4 cup butter and 1/2 cup cream, something in the range of 8 to 10 oz of sliced mushrooms is a reasonable modern proportion; much less and the sauce will be thin.
• "Sweet butter"This means unsalted butter, not sweetened. Since the recipe gives no salt at all, season the mushrooms as they stew and taste again before serving.
• "Rich cream"Cream so described was unstandardised but generally much fatter than today's light cream, closer to modern heavy cream. Half-and-half or light cream will not reduce to a coating consistency as readily and is more prone to separating.
• "Boil until tender"Cultivated mushrooms are tender in 5 to 8 minutes of gentle simmering, not the longer cooking the wording suggests. Watch the milk, which scorches easily; keep the heat moderate and stir.
• The flour alternativeThe cross-reference to oyster toast presumably points to a thickening of flour slaked in cold milk. Roughly 1 tablespoon flour to 1 cup liquid gives a creamy sauce, and it needs a minute or two at the boil to lose the raw taste -- the opposite of the egg-yolk method.
• ToastCut it thick and butter it hot, and assemble at the last moment; thin toast goes soggy quickly under a cream sauce.
• YieldAs written it will probably cover two to four slices, depending on how much mushroom you use.