Preheat oven to 350°F. Line an 8-inch square baking pan with parchment, letting the ends extend up the sides. In a large bowl, combine the graham cracker crumbs, sugar, and melted butter until moistened. Press into the prepared pan. Bake until the edges begin to brown, about 10 minutes. Remove to a wire rack to cool completely. In a large bowl, beat the cream cheese and sugar until smooth. Add the pistachio cream, milk, and vanilla extract until incorporated. Beat in the egg until just combined. Pour over the cooled crust. Bake until the center is almost set, 20 to 22 minutes. Remove to a wire rack to cool completely. Cover and refrigerate at least 4 hours or overnight. To make the kataifi layer, melt the butter in a skillet over medium-low heat. Toast the kataifi in the butter until golden brown, 6 to 8 minutes; let cool. In a large bowl, stir together the toasted kataifi, pistachio cream, and tahini. Spread the kataifi layer evenly over the chilled cheesecake; place back in the refrigerator. To make the ganache, place the chopped chocolate in a heat-safe bowl. In a small saucepan, heat the heavy cream to a low simmer. Pour the cream over the chocolate; wait 1 minute, then whisk until smooth. Pour the ganache over the kataifi layer. Cover and refrigerate at least 1 hour. Pull the bars from the pan using the parchment sides, slice, and serve. If desired, garnish with crushed pistachios.