How to cook
The dark green part of the watermelon peel is removed with a potato peeler. The peels are washed and the white part is cut into cubes. Each cube is pierced with a fork.
Dissolve the soda in a glass of hot water. Put the peels in a pot and pour the dissolved soda. Add another 6 glasses of water.
Stir and leave them for 4 hours. The water is poured out and the peels are washed well. Pour them cold water, leave them for 30 minutes and wash them well. Prepare a sugar syrup from half the sugar and 3 cups of water. Heat it over medium heat to a boiling point.
Put the cubes in the syrup and boil them medium heat for 20 minutes, while stirring occasionally. Remove it from the heat and leave it for 12 hours. Add the remaining sugar.
Heat it over medium heat to boiling point and leave it to boil for 30 minutes, while stirring occasionally. Leave it again for 12 hours, then heat it to a boiling point and boil it for 20 minutes. The jam is distributed, while it's hot, into dry and clean jars.