Melt the butter and add it. Mix well until a homogeneous mixture is obtained.
Line the bottom of a cake pan (diameter 22 cm) with parchment paper. Transfer the mixture, pressing it to form an even layer. Leave it in a refrigerator for 30 minutes.
In a large bowl, beat the yoghurt together with the mascarpone.
Wash and peel the cucumber, then cut it into small cubes. Add the salt, the minced garlic, the chopped dill and the oil. Mix it.
Add to the yogurt and mascarpone mixture. Mix it.
Put the gelatine sheets in a bowl with cold water and leave for about 10 minutes.
In a small saucepan, heat the milk. Add the gelatine well squeezed out of the water and stir with a spoon to dissolve it completely. Heat over low heat, being careful not to boil it. Remove from heat and leave it to cool.
Gradually drizzle the dissolved gelatine into the other mixture, whisking gently.
Pour the cream into the cracker crust. Leave it in a refrigerator for at least 3 hours.
Gently remove the cheesecake from the cake pan and decorate it as desired with walnuts, dill and cucumbers.