Blackberry Jam Custards

This is a jam custard pie filling in shorthand — the kind of note-form recipe Mrs. Wilson wrote for readers who already knew how a pie was assembled. Everything it leaves out is standard practice for the period.

• What you are actually makingCream the softened butter with the sugar, beat in the eggs, then fold in the jam. Pour into a raw pastry shell and bake. It sets like a chess or transparent pie — soft, glossy, sliceable when cold, not a stirred custard.
• Quantities and yieldThe filling would suit roughly one 9-inch shell; it is generous, so a deep-dish shell is safer than a shallow one. Half a cup of butter is one stick, 4 oz.
• Oven heatNo temperature is given, which is normal for recipes written in this note form. As a modern reconstruction: start at 425F for about 15 minutes to set the pastry, then drop to 325-350F for another 25-35 minutes, until the center is puffed but still trembles slightly. It firms as it cools.
• The hinge: do not overbakeSugar-and-butter custards of this type crack and weep if taken past just-set. Pull the pie while the middle still moves; residual heat finishes it.
• Whole eggs versus yolksWith four whole eggs there are no whites left over, so the meringue needs two or three extra whites and 1 to 2 tablespoons sugar per white, browned briefly in a hot oven. The yolks-only version gives a richer, denser filling; the recipe does not say how many yolks to use. Cream icing — in period usage generally confectioners' sugar beaten with cream, sometimes with butter — goes on after the pie is completely cold or it will slide.
• The jam mattersBlackberry jam of this period was generally boiled to a firm set and left seedy, and tended to be less sweet than many modern jams. A modern soft-set or low-sugar jam carries more water; if yours is very sweet, cut the sugar to three-quarters of a cup and add a teaspoon of lemon juice.