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1
The day before you wish to make the jam, hull and halve the strawberries.
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2
Check for soft spots (which must be removed) and discard any berries with bruises or that are overripe.
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3
Place the strawberries into a large bowl with 500g/18oz of the sugar.
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4
Turn carefully to mix and coat well, then cover with cling film and place into the fridge overnight.
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5
The next day, place a saucer into the freezer to chill - you'll need this when you come to test the setting point of the jam.
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6
Sterilise the jam jars - first wash the jars in soapy water and rinse in clean warm water.
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7
Allow them to drip-dry, upside down, on a rack in the oven set to 140C/275F/Gas 1.
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8
Leave them there for at least half an hour while you make the jam.
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9
Pour the strawberries, their juice and any residual sugary juices into a very large pan or preserving pan, remembering that the mixture will rise as it boils, and add the remaining 500g/18oz sugar and the lemon juice.
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10
Stir over a gentle heat until the sugar has completely dissolved.
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11
Bring the strawberries up to the boil then boil hard until the jam reaches setting point.
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12
Check the setting point every ten minutes, although it may take up to half an hour to reach setting point.
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13
To test the setting point, remove the pan from the heat.
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14
Take your saucer from the freezer and place a drop of jam onto the cold plate.
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15
After a few seconds push the jam with your finger.
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16
If the jam surface wrinkles then it has reached setting point and is ready.
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17
If it slides about as a liquid, then it hasn't reached setting point and should be returned to the heat and boiled for a few more minutes before testing again.
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18
When setting point has been reached, turn off the heat.
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19
Stir in the butter and skim off any scum on the surface of the jam with a large spoon.
