Combine all the ingredients in a clean and dry stand mixer bowl. Make sure the bowl is really clean as residues will inhibit the egg whites from whipping.

Beat (using the whisk attachment) at maximum speed for at least 5 minutes or until hard peaks form.

Serve in individual glasses (I use a piping bag for a beautiful swirl effect) decorated with mint or lemon balm leaves and some extra lingonberry jam if desired. The mousse has to be consumed within 24 hours or the egg whites will start to separate and collapse.