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1
Preheat the oven to 350 degrees F.
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2
To make the base, process the graham crackers to make rough crumbs and then add the butter and cocoa.
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3
Process again until it makes damp, clumping crumbs and then tip them into the pan.
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4
Press the crumbs into the bottom of the pan to make an even base and put into the freezer while you make the filling.
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5
Put a kettle on to boil.
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6
Melt the chocolate either in a microwave or double boiler, and set aside to cool slightly.
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7
Beat the cream cheese to soften it, then add the sugar and custard power, beating again to combine.
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8
Beat in the whole eggs and then the yolks, and the sour cream.
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9
Finally add the cocoa dissolved in hot water and melted chocolate and mix to a smooth batter.
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10
Take the springform tin out of the freezer and line the outside of the tin with a good layer of cling wrap, and then another layer of strong foil over that.
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11
This will protect it from the water bath.
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12
Sit the springform tin in a roasting pan and pour in the cheesecake filling.
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13
Fill the roasting pan with just boiled water to come about half way up the cake tin and bake in the oven for 45 minutes to 1 hour.
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14
The top of the cheesecake should be set, but the underneath should still have a wobble to it.
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15
Peel away the foil and cling film wrapping and sit the cheesecake in its tin on a rack to cool.
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16
Put in the refrigerator once it is no longer hot, and leave to set, covered with plastic overnight.
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17
Let it lose its chill before unspringing the cheesecake to serve.
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18
To make the chocolate sauce: very gently melt the chopped chocolate, cream and syrup.
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19
When the chocolate has nearly melted, take off the heat and whisk it to a smooth sauce.
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20
Let it cool a little, and pour it over the chocolate cheesecake on its serving plate.
