Chop the strawberries: Remove the green tops, then cut the strawberries into smaller pieces. This helps them break down faster once they start cooking.
Start cooking the fruit: Place the chopped strawberries in a large pot. In a small bowl, stir the packet of Gelfix Super with 2 tablespoons of the sugar. Add that mixture to the pot and stir everything together.
Bring to a boil: Set the pot over medium-high heat. While stirring, bring the strawberries to a full boil and let them cook for 1 minute.
Add the rest of the sugar: Pour in the remaining sugar, stir well, and bring the mixture back to a boil. Keep stirring and let it cook for about 5 minutes.
Skim off any foam: If foam rises to the top, skim it off with a spoon and discard.
Pour the jam into the jars: Immediately pour the hot cooked jam into clean jars while it’s still piping hot. USDA recommends leaving 1/4" of headspace, so fill the jam to just below the rim.
Seal and flip: Wipe the rims clean, close the jars with lids, and turn them upside down. Leave them flipped while they cool; this little trick helps the lids seal as the jam sets.