How to cook
Remove the strawberries' stems and wash them. Use whole, healthy strawberries without any damage on their surface. Don't use rotten fruits.
Leave smaller fruits whole, cut larger ones in half. Put 1/2 of them in a deep bowl, pour 1/2 the sugar over them, cover with the remaining strawberries and remaining sugar. Leave the bowl in the fridge overnight. The next morning, the strawberries will have released juice.
Transfer the entire contents of the bowl into a deep pot and put it on the stove. Boil the jam while stirring carefully, taking care to keep most of the fruits whole. Once it reaches boiling point there's going to be foam, remove it with spoon. The more foam you remove, the clearer your jam will be.
Boil until thickened. Check by pouring a drop of it onto a plate or into a glass of cold water, it must not run. Add 1 tsp citric acid and stir. Remove from the heat.
Prepare clean and dry jars. Heat them slightly in a 120°F (50 °C) oven if possible so they don't crack when you fill them. While still hot, distribute the jam into the jars, try to get whole fruits in each one.
Close with the caps and turn upside down. Leave it as is for 2 days, then store in a cool, ventilated area.