The old-favourite vanilla slice gets a twist here with the addition of Nutella and coffee and chocolate in the icing. Getting the icing right is important - too thick and it won't spread; too thin and it will run off. You can eat this freshly sliced, but it's quite sticky; best to let it set in the fridge first if you have time. Start this recipe a day ahead to make the hazelnut custard. This recipe makes about 10 pieces.
- 1 sheet butter puff pastry (375gm; see note)
- 2 tbsp chocolate hazelnut spread (such as Nutella), for spreading
- 500 ml (2 cups) milk
- 350 ml pouring cream
- 150 gm roasted peeled hazelnuts
- 100 gm caster sugar
- 6 egg yolks
- 2 tbsp each cornflour and plain flour
- Scraped seeds from 1 vanilla bean
- 70 gm butter, softened
- 160 gm pure icing sugar, sieved
- 1 tbsp Dutch-process cocoa, sieved
- 3 tsp espresso-strength coffee
- 1 tbsp pouring cream mixed with 1 tbsp water
- 1For hazelnut custard, bring milk, cream and hazelnuts to the simmer in a saucepan over medium-high heat. Set aside to cool (1 hour), then refrigerate until chilled and infused (4 hours or overnight). Strain hazelnut milk into a clean saucepan and bring to the simmer over medium-high heat. (Discard hazelnuts, or dry them in a low oven and reserve for another use.) Meanwhile, whisk sugar and yolks in a bowl until pale, then add flours and vanilla seeds, and whisk to combine. Gradually pour hot milk mixture into yolk mixture while whisking, then return to pan and whisk over medium-high heat, ensuring you reach the corners of the pan, until thick and bubbling (5-7 minutes). Set aside to cool briefly (5-7 minutes), then whisk in butter and set aside.
- 2Preheat oven to 200C. Roll puff pastry to a rectangle about 40cm x 28cm and 3mm thick. Cut into 2 equal rectangles of about 20cm x 14cm. Prick all over with a fork, then place each piece of pastry between 2 sheets of baking paper then 2 oven trays and bake, turning trays halfway through cooking, until pastry is golden and crisp (25-35 minutes). If pastry cooks unevenly, remove top tray and continue baking and turning pastry until dry and crisp. (If you don’t have enough trays, cook pastry sheets one at a time.)
- 3Place a piece of pastry on a tray lined with baking paper. Spread with hazelnut spread, top with custard and spread to just short of the edges, then sandwich with remaining piece of pastry and refrigerate until custard is set and firm (4 hours or overnight).
- 4For coffee-chocolate icing, stir 30gm icing sugar, cocoa and coffee in a bowl, adding more icing sugar or coffee as necessary until mixture is a thick spreading consistency. Set aside. Stir cream mixture with remaining icing sugar in another bowl, adding water if necessary until it’s a thick spreading consistency. Spread white icing evenly over slice, then dot dark icing all over. Swirl a skewer through dark icing to create a pattern, then refrigerate until icing sets (1½-2 hours). Trim edges with a serrated knife and cut into slices. Slice will keep refrigerated in an airtight container for 1-2 days.
Note We prefer to use Carême butter puff pastry, which comes in 375gm sheets.