Mix yolks, icing sugar, yogurt, lemon juice, 2/3 of the gelatin powder, half of the whipping cream in a pot and bring to simmer. Cool to room temperature
Once mixture is cooled, mix in 2/3 of the mandarin slices, and pour onto cooled cake. Chill in the fridge to firm up for at least 3 H.
Release cake from the spring-form pan and cover the sides of the cake with almond meal
Beat the rest of the whipping cream and gelatin powder with a little icing sugar. Cover the top of the cake.