Soak the gelatin leaves in cold water.
Crush the cookies in a for example food processor, and mix in sea buckthorn powder and melted margarine.
Place baking paper on the bottom of a springform pan (diameter approx. 24 cm) and press the biscuit mixture onto the bottom of the pan.
Put in the fridge to harden.
Mix the yogurt and sugars.
Squeeze the gelatin leaves and dissolve them in 1/2 deciliter of sea buckthorn juice. Add the remaining 1/2 dl of sea buckthorn juice.
Mix the gelatin mixture in a smooth strip into the yogurt, stirring all the time. Finally, add the whipped cream, stirring gently.
Pour the mixture on the pan and let it set in the fridge overnight.
Prepare the decorative jelly by boiling water and sea buckthorn juice in a pot. Add the jelly sugar and bring the mixture to a boil, cool slightly. Carefully spread the decorative jelly with a spoon on top of the cream jelly. Let it set for a while in the fridge and decorate with for example edible flowers.