4 pounds ripe apricots (include a few underripe fruits to help jam gel)
6 cups (2 pounds, 8 ounces) granulated sugar
1/3 cup strained fresh lemon juice
2 teaspoons butter
Halve the apricots and remove pits. Cut each half into quarters.
In a large, nonaluminum bowl, layer apricots with the sugar. Drizzle on the lemon juice, then gently stir and toss mixture to thoroughly disburse sugar. Apricots will begin to release juices, and sugar will begin to dissolve.
Cover bowl with foil or plastic wrap and refrigerate for 1 to several hours, stirring occasionally to encourage sugar to dissolve.
IF PREPARING FOR THE FREEZER: Scrape mixture into an appropriate-sized freezer container, label carefully (noting amount, when frozen and any other instructions for finishing jam) and freeze. When ready to make into jam, simply thaw and proceed as directed below.
Wash 8 half-pint jars. Keep hot until needed. (I place a clean kitchen towel on a baking sheet in a 170-degree oven and store jars there until needed.) Prepare 2-piece canning lids as manufacturer directs.
Scrape apricot mixture into a large, wide, heavy-bottomed pot, wide enough to encourage rapid evaporation of water in fruit, and deep enough to contain a vigorous, rolling boil)
Add the butter and bring mixture to a boil, then adjust heat to a simmer that can't be stirred down. Cook, uncovered, for 15 minutes, stirring almost continuously with a heatproof spatula or flat-ended wooden spoon to keep jam from scorching on bottom. Don't worry about foam produced during this phase; most will disappear toward end of cooking.
After 15 minutes of cooking, you have to use a bit of judgement to determine if jam is reaching the "gelling point," where it turns from fruit in sugar to a substance that will thicken when cooled and stay thickened. For this particular jam, I've found the gelling point to be about 218 F (at sea level). So once surface begins to look very "glisteny" and bubbles seem larger, thicker and shiny, stick a candy thermometer into mixture and start monitoring temperature. You're looking at another 2 to 7 minutes of cooking, depending on how juicy a mixture you started with, and how rich in natural pectin the fruit is.
When jam reaches 218 F, remove pot from burner and let preserves sit for about 1 minute. If any foam remains on surface, most of it will be absorbed back into jam. With a spoon, skim off any foam that has not settled back into mixture.
Ladle hot preserves into 1 hot jar at a time. Wipe rim with a clean, damp cloth. Attach lid and ring, turning firmly for a good seal (jar will be very hot, so use a pot holder or towel where your hand comes in contact with it). Repeat with remaining jars and lids.
At this point, jam may be stored in refrigerator (after cooling overnight on countertop) for up to 12 months without quality suffering.
For long-term storage at room temperature, process jars in a boiling-water canner for 10 minutes (for 15 minutes at 1,000 to 3,000 feet; for 20 minutes at 3,000 to 6,000 feet; for 25 minutes above 6,000 feet). Using a jar lifter, remove processed jars from boiling water and let cool on counter, undisturbed, overnight. Makes 7 to 8 half-pints of jam.