Mix graham cracker crumbs, 1/2 cup sugar, butter, and 2 tablespoons tahini together in a bowl. Press into the bottom of a 10-inch springform pan. Sprinkle 1/4 crushed pecans over the prepared crust.
Place cream cheese in a large bowl. Beat in egg until smooth. Beat in egg yolk. Mix in sour cream and vanilla extract. Add 1 1/4 cups sugar, heavy cream, and flour; blend until smooth. Spread 2 cups of batter over the crust to form the first filling layer.
Stir pumpkin puree, cinnamon, cloves, and nutmeg into the remaining batter in the bowl. Spread over the first layer of filling.
Place cheesecake in a cold oven. Set oven temperature to 200 degrees F (95 degrees C). Bake cheesecake until set, 3 hours and 10 minutes. Crack the oven door open and let cheesecake cool inside for 1 hour. Refrigerate until firm, 8 to 24 hours.
Spread 1/4 cup tahini over the surface of the cheesecake; arrange pecan pieces decoratively on top.