How to Make It
Chop your rye bread into chunks and mix with the remaining ingredients in a large mixing bowl. Let sit overnight.
Cook the soaked rye bread mixture over medium heat for 20 to 30 minutes, stirring occasionally. Cool and reserve until ready to use.
To make the skyr mousse, start by mixing the cream, yolks, and sugar and cook over a double boiler, stirring constantly, until the mixture has thickened. Cool in an ice bath and add skyr and salt. Place in a siphon (also known as a whipped cream dispenser) and charge with NO2 (nitrogen peroxide). Shake well. This can also be made in advance up to 1 week.
Heat the porridge back up and finish with heavy cream to taste. Garnish with grated chocolate and lemon zest.