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1
In a small saucepan combine the sugar, heavy cream, buttermilk, cornstarch and pinch of salt, and whisk until smooth.
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2
Place over medium-high heat, and bring to a boil, whisking from time to time, for the sugar and cornstarch to dissolve and the mixture to thicken, about 5 minutes.
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3
Continue cooking at a low boil for an additional 5 minutes, whisking constantly.
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4
In a mixing bowl, beat the egg yolks lightly.
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5
Pour 1/2 cup of the hot mixture into the egg yolks and whisk thoroughly.
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6
Pour the egg yolk mixture into the saucepan and whisk over the heat into thoroughly combined, about 30 seconds.
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7
Pour the mixture into a mixing bowl, and whisk in the chocolate, butter and vanilla.
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8
Continue whisking until thoroughly combined (mixture will be very thick).
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9
Pour the chocolate batter into the prepared pie crust and refrigerate until firm and cool, at least 4 hours.
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10
Preheat oven to 375 degrees F.
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11
In the bowl of a food processor or blender, process the graham crackers and Oreos to make crumbs.
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12
In a bowl mix together the cookie crumbs, sugar and butter with your hands.
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13
Press the mixture evenly into a 9-inch pie pan.
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14
(It will seem like an excessive amount of crumbs, but it will compress down quite a bit with pressure.)
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15
Cover the crust with plastic wrap and top with another 9-inch pan, pressing quite firmly to make a smooth surface.
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16
Bake the crust for 15 minutes.
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17
Remove the crust from the oven and let cool completely before filling.
