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1
Oil and line a 28 x 18 x 2.5 cm cake tin with non-stick baking parchment.
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2
Place the 75g butter and 125g chocolate in a heatproof bowl set over a saucepan of almost boiling water until melted stirring occasionally.
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3
Stir in the crushed biscuits, coconut and nuts into the chocolate mixture and mix well.
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4
Spoon into the prepared tin and press down firmly.
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5
Chill in the refrigerator for 20 minutes.
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6
For the icing place the egg yolk and milk in a heatproof bowl set over a saucepan of almost boiling water, making sure the bowl does not touch the water.
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7
Whisk for 2-3 minutes.
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8
Add the 75 g butter and vanilla essence to the bowl and continue whisking until fluffly, then gradually whisk in the icing sugar.
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9
Spread over the chilled base, smoothing with the back of a spoon and chill in the refrigerator for a futher 30 minutes.
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10
For the topping, place the 125g chocolate and sunflower oil in a heatproof bowl set over a saucepan of almost boiling water.
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11
Melt, stirring occasionally, until smooth.
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12
Leave to cool slightly then pour over the filling and tilt the tin so that the chocolate spreads evenly.
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13
Chill in the refrigerator for about 5 minutes, or until the chocolate topping is just set but not too hard, then mark into 15 bars.
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14
Chill again in the refrigerator for 2 hours, then cut into slices and serve.
