Hazelnut Chocolate Bars

1. Soak 40g / 1.41oz pitted soft dates in water for 30 minutes, drain, and puree with 50g / 1.76oz apple puree.
2. Preheat the oven to 200°C (392°F).
3. Whisk 3 eggs until frothy for about 3 minutes.
4. Stir in the date-apple mixture.
5. Add 100g / 3.53oz flour, 2 tsp cream of tartar, 25g / 0.88oz cornstarch, and 20g / 0.71oz cocoa powder, and mix briefly.
6. Spread the batter evenly on a baking sheet lined with parchment paper (22x28 cm).
7. Bake for about 18 minutes.
8. Remove from the oven, turn onto a cake rack, and carefully peel off the parchment paper.
9. Halve the sponge cake both crosswise and lengthwise and let cool for about 1 hour.
10. Whip 200g / 7.05oz cream until stiff.
11. Carefully fold in 50g / 1.76oz ground hazelnuts.
12. Spread half of the filling evenly on two sponge pieces.
13. Place the remaining sponge pieces on top.
14. Freeze the slices for about 50 minutes.
15. Halve the cake sandwiches with a sharp knife and cut into four parts lengthwise. Serve immediately or store in the refrigerator.