Classic Strawberry Jam

From the garden

• 3 lb ripe strawberries, hulled — about 2 quarts, to yield 5 cups crushed

From the pantry

• 7 cups granulated sugar — measured out in advance — it goes in all at once; don't reduce it
• 1¾ oz powdered fruit pectin — one standard box
• ¼ cup bottled lemon juice

1. Fill a boiling-water canner and bring it to a simmer. Wash 8 half-pint jars and keep them hot in simmering water; prepare the lids according to the manufacturer's directions. Measure the sugar into a bowl so it's ready to add in one go.
2. Crush the hulled berries one layer at a time with a potato masher and measure exactly 5 cups into a tall, heavy pot — jam foams high, so the pot should be no more than a third full. Stir in the lemon juice and the pectin.
3. Bring to a full rolling boil over high heat, stirring constantly — a boil that keeps rolling while you stir. Add all the sugar at once, return to a full rolling boil, and boil hard exactly 1 minute, still stirring. Off the heat, skim the foam.
4. Ladle the hot jam into the hot jars, leaving 1/4 inch of headspace. Wipe the rims with a damp cloth and screw on the lids to fingertip-tight.
5. Process in the boiling-water bath, jars covered by 1–2 inches of water, for 10 minutes at a steady boil. Altitude adjustment: add 5 minutes at 1,001–6,000 feet, 10 minutes above 6,000 feet. Turn off the heat, rest 5 minutes, then lift the jars out.
6. Cool undisturbed 12–24 hours, then check the seals — lids should be concave and not flex. Remove the bands, label and date, and refrigerate any jar that didn't seal. The set finishes as the jars cool; don't tip them to check.