Mix flour, potato flour, and baking powder.
Whip eggs, vanilla, and sugar into a fluffy eggnog mixture.
Sift the flour mixture and fold it in with lemon zest.
Spread on a baking sheet and bake at 225 degrees Celsius (437 degrees Fahrenheit) in a conventional oven for 6-8 minutes.
Turn the bottom with the top down onto a sugar-sprinkled parchment paper.
Pull off the parchment paper and let cool under a damp cloth.
Boil the jam with lemon juice in a pot until about 2.5-3 dl remains.
Let cool completely.
Soak gelatin in water. Whisk cream cheese, powdered sugar, zest, and 1 tbsp lemon juice together.
Whip the cream until slightly stiff in another bowl.
Squeeze out the water from the gelatin and melt with 1 tbsp lemon juice in the microwave.
Mix with the cream cheese mixture and fold together with the whipped cream.
Spread the jam on the base and then the cream.
Leave a 2 cm edge free of the cream.
Roll the Swiss roll using the parchment paper, and place the roll seam side down in the refrigerator.
Boil water and sugar to 115 degrees Celsius (239 degrees Fahrenheit).
It should be thick.
Whisk egg whites stiff and pour the piping-hot syrup in a thin stream while continuing to whisk.
Whisk until firm and stiff for 8-10 minutes.
Save 2/3 of the meringue for the Swiss roll.
Pipe the remaining 1/3 into mushroom shapes. (Nozzle 12 mm round) Half should be large and flat, and the other half taller and thinner.
Sprinkle raspberry powder on the tops.
Bake at 110 degrees Celsius (230 degrees Fahrenheit) for about 70 minutes with fan.
Melt chocolate and use it as glue between the mushroom tops and bottoms.
Trim the roll. Spread the meringue and use a stick/fork to create bark patterns.
Burn with a blowtorch.
Decorate with the mushrooms.
Enjoy.
