The day before (J-1): Prepare the ganaches. For the Nutella ganache, chop the chocolate and add to a bowl with Nutella. Microwave for 30 seconds, mix partially melted chocolate. Boil 100g cream, pour over the chocolate mix in two additions, stirring each time. Add 50g cold cream, mix, and then the remaining 25g cream. Mix and blend until smooth. Cover with cling film and refrigerate overnight. For the white chocolate ganache, microwave the broken white chocolate for 30 seconds, soak gelatin in cold water, heat 200g cream (do not boil), dissolve gelatin in hot cream, pour over chocolate in three additions, stirring constantly, add remaining 220g cream, blend if necessary, cover and refrigerate overnight.
On the day (Day J): In a mixer, blend flour, cold chopped butter, and icing sugar to a sandy texture. Add egg, mix at low speed just until combined. Chill the dough for 1 hour. Roll out to 3mm thickness on parchment paper, cut out the digit shapes, remove excess dough. Freeze shaped dough on a baking sheet until oven preheats to 170°C with fan. Prick dough all over with a fork, bake for 18 minutes on two racks, removing silicone mats 4 minutes before end. Cool completely on a flat surface.
Mounting the ganaches: Chill mixing bowl and whisk for 30 minutes. Whip vanilla ganache to soft peaks, fill a piping bag fitted with a smooth large tip. Repeat with Nutella ganache using a ridged tip. Layer one digit of sweet dough on a serving plate, pipe ganaches, starting with a base of white chocolate and adding Nutella ganache accents. Top with second digit, pipe ganaches to cover, decorate with Kinder chocolates and chocolate balls.
Serve: Refrigerate until serving. Best consumed within 24 hours.