Wash the strawberries (do not put them under running water, wash them in a basin), then cut their tails and put them on a kitchen towel to dry.
Put the strawberries, 1 kg of sugar and the peel of a lemon in a large pot (large pieces, not grated because it has to be removed), then cover and leave to cool overnight.
The next day we remove the lemon peel and put the rest of the sugar and the juice from the 2 lemons.
Put on low heat for 45-50 minutes (stir from time to time) after which we test to see if it is ready (we put it on a saucer to cool and if it does not flow it is ready), otherwise we leave it until it is of the desired consistency .
Meanwhile, wash the jars and put them in a tray (with lids), then put them in the oven at 100 ° -125 ° for 15-20 minutes.
When the jam is ready, put it hot in the jars (we put a knife under the jar when we put the jam so that it doesn't crack), put the lids on and turn the jars upside down until they cool.
When you turn them you will hear a click, a sign that they are closed well and you can keep them for the winter (if they catch).