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1
Preheat the oven to 350u00b0F (180u00b0C). Lightly butter a deep 9-inch pie pan.
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2
Roll out the dough into a 12-inch circle on parchment paper or a silicone mat. Slide one hand underneath the parchment, slightly lifting the center of the dough. Pick up the pie pan in your other hand, and invert it over the dough, pressing the center of the dough into the center of the pan, then carefully flip over the pie pan and the dough. Lift off the parchment paper and discard. Gently press the dough against the bottom and sides of the pan. Trim the edges, leaving a 1-inch overhang. Tuck the overhang under the crust, forming a soft cylinder of dough all the way around the pie. Use your thumbs and forefingers to gently pinch and crimp this dough all the way around to form the border.
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3
Bake the crust for 30 minutes. Rotate the pan and bake for 10 more minutes, or until the crust is a deep brown. Put the pan on a wire rack and let cool completely.
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4
Put the blueberries, sugar, and salt in a medium saucepan and bring to a simmer over medium heat. Reduce heat to low and cook for 10 minutes, until the berries begin to burst and become juicy.
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5
Meanwhile, put the tapioca starch, cornstarch, and water in a small bowl and stir to make a slurry. Increase the heat to medium, pour in the slurry, and cook, stirring constantly, until the mixture comes to a boil and thickens, about 5 minutes. Remove from the heat and let cool.
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6
Put the sour cream, sugar, and salt in a blender and blend on low until smooth. Add egg and blend just until incorporated. Add the vanilla and blend to incorporate. Add the cream cheese and blend until smooth. With the blender running, pour in the melted butter and blend until the butter has been absorbed. Set aside.
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7
To make the streusel, put the sugar, flour, lavender (if using), and salt in a food processor and pulse to a fine powder, about 30 seconds. Add the butter and pulse until the mixture resembles coarse meal. Reserve in a covered container in the refrigerator.
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8
Pour the blueberry layer into the baked pie crust, using a small offset spatula to spread it evenly on the bottom. Pour the cheesecake layer over the blueberry layer. Put the pie in the oven and bake for 15 minutes.
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9
Remove from the oven and carefully sprinkle the streusel over the top of the pie. Return to the oven and bake for another 40 minutes, until the filling is just set but still wobbles slightly when shaken gently; the internal temperature of the cheesecake layer should be 150u00b0F (66u00b0C). Let the pie cool completely. Transfer the pie to the refrigerator and chill for at least 3 hours before serving.
