• Prepare the strawberries by wiping them with a piece of damp kitchen paper. (Wiping the strawberries rather than washing them ensures the fruit doesn’t absorb lots of water – too much water and the jam won’t set easily.) To hull the fruit, use a knife to cut a cone shape into the strawberry and remove the stem. Cut any large berries in half.
• Put the strawberries in a bowl and gently toss through the sugar. Leave uncovered at room temperature for 12 hrs or overnight. This process helps the sugar to dissolve, ensures the fruit doesn’t disintegrate too much and helps to keep its vibrant colour.
• Before starting the jam, put 2 saucers in the freezer. Tip the strawberry mixture into a preserving pan with the lemon juice. Set over a low heat and cook very gently. If any sugar remains on the sides of the pan, dip a pastry brush in hot water and brush the sugar away.
• When you can no longer feel any grains of sugar remaining, turn up the heat to start bubbling the jam and bringing it to the boil. (The sugar must be completely dissolved before increasing the heat, otherwise it will be difficult for the jam to set, and it may contain crystallised lumps of sugar.)
• Boil hard for 5-10 mins until the jam has reached 105c on a preserving or digital thermometer, then turn off the heat. If you don’t have a thermometer, spoon a little jam onto one of the cold saucers. Leave for 30 secs, then push with your finger; if the jam wrinkles and doesn’t flood to fill the gap, it is ready. If not, turn the heat back on and boil for 2 mins more, then turn off the heat and do the wrinkle test again. Repeat until ready.
• Use a spoon to skim any scum that has risen to the surface and discard this. Do this only once at the end, rather than constantly during the boiling stage, to reduce wastage.
• Add a knob of butter, if you like, to the finished jam, and stir in to melt. This will help to dissolve any remaining scum that you haven’t managed to spoon off the top. Leave the jam to settle for 15 mins – this will ensure that the fruit stays suspended in the mixture and doesn’t all float to the top of the jam jar. Meanwhile, sterilise your jars.
• Ladle into warm jars, filling to just below the rim. Place a wax disc on top of the jam (this prevents mildew forming), then cover with a lid or a cellophane circle and elastic band. Pop on a label (include the date), plus a pretty fabric top, if you like. The jam can be stored for up to 1 year in a cool, dry place. Refrigerate after opening.

Recipe from BBC GoodFood