For finishing
Carefully drain the pears and dry them with a paper towel.
Melt the white chocolate in pieces with the butter and hazelnut puree. Mix well and add 6 egg yolks.
Beat 4 egg whites with salt in a mixer until stiff and fold in gently with a spatula.
Line a log mould with cling film. Fill halfway with hazelnut mousse and place the pear halves upside down in the mould, immersing them in the mousse. Top up with the rest of the mousse. Store in the freezer for 6 hours.
Break up the dark chocolate and melt it with the butter and water. Turn the frozen log out onto a wire rack and drizzle with the slightly cooled chocolate icing to create a thin layer. Transfer to a serving dish. Leave to set in the fridge and defrost the log for 6 hours.
Just before serving, sprinkle the top of the log with popping candy.