Step 1: Prepare the Strawberries. Wash fresh strawberries thoroughly, hull them, and quarter them (or slice smaller for a smoother jam, larger for a chunkier jam). Measure out 4 cups of prepared strawberries.
Step 2: Macerate the Strawberries. In a large, heavy-bottomed pot, combine the prepared strawberries and granulated sugar. Stir gently until sugar is evenly distributed. Cover and let sit at room temperature for 2-4 hours, or overnight in the refrigerator, to draw out the fruit juices.
Step 3: Start Cooking. Add the fresh lemon juice to the strawberry-sugar mixture. Place the pot over medium-high heat and bring to a rolling boil, stirring frequently to prevent scorching.
Step 4: Skim and Boil. Once a rolling boil is achieved, reduce heat slightly to maintain a vigorous boil. Continue to cook, stirring occasionally and skimming off any foam that rises to the surface, for 20-30 minutes.
Step 5: Test for Set. To check if the jam is set, use the cold plate test (spoon a small amount onto a frozen plate, wait 1 minute, then push with your finger; if it wrinkles, it's ready) or a candy thermometer (jam should reach 220°F / 104°C).
Step 6: Ladle into Jars. Remove the pot from heat. Carefully ladle the hot jam into hot, sterilized canning jars, leaving 1/4 inch of headspace. Wipe rims clean, then place lids and screw on bands finger-tight.
Step 7: Process Jars (Optional). For long-term shelf stability, process jars in a boiling water canner for 10 minutes. Remove and let sit for 5 minutes before taking out.
Step 8: Cool and Store. Place jars on a wire rack to cool undisturbed for 12-24 hours. Check seals (lids should not flex). Store sealed jars in a cool, dark place for up to a year. Refrigerate unsealed or opened jars and consume within 3 weeks.