This is seriously impressive, but incredibly simple to make – it’s worth using good-quality chocolate to achieve the best flavour
- 250g (9oz) very good-quality dark chocolate, around 85% cocoa solids (we used Lindt Excellence)
- 250g (9oz) caster sugar
- 250g (9oz) unsalted butter
- zest 3 oranges
- 2tbsp plain flour
- 4 large free-range eggs
- generous pinch sea salt
- icing sugar and 60g (2½oz) hazelnuts, toasted and roughly chopped, to serve
- 25cm (10in) watertight tart tin, buttered and dusted with cocoa, and the bottom lined with baking parchment
Heat the oven to 150C, 130C fan, 300F, gas 2. Place the chocolate, sugar, butter and orange zest in a heavy-bottomed saucepan and heat very gently, stirring occasionally until melted. With a hand whisk, stir in the flour and then the eggs, one by one, until you have a smooth mix. Don’t worry if it curdles – keep stirring and adding the eggs, and it will come back together. Finally stir in the salt.
Spoon the mix into the tin, and place in a roasting tin of hot water, making sure the water level is at least 1cm (½in) below the top of the tart tin. Cook in the centre of the oven for 50 minutes to 1 hour, until the top of the tart is springy to the touch.
Remove from the oven and the roasting tin, allow to cool a little then invert on to a serving platter. You can eat this warm, or allow to cool to room temperature. To serve, sift over a little icing sugar, and scatter with hazelnuts. This will keep overnight, but is best on the day it’s made.