Prepare the berries and sugar. Rinse fresh or frozen lingonberries and place them in a large pot with the sugar and water. Stir to combine
Boil and cook. Bring the mixture to a boil over medium heat, then reduce to a gentle simmer. Cook for about 30 minutes, stirring often, until the berries soften, become translucent and begin to thicken.
Optional blending. If you prefer a smoother jam, use an immersion blender to pulse the mixture. Test for doneness by placing a spoonful of jam on a chilled plate; if it gels after a minute, it’s ready.
Jar and seal. Pour the hot jam into sterilised glass jars, leaving a little headspace. Screw on the lid and turn the jars upside down to create a vacuum. Allow to cool completely, label and store in a cool, dark place.
