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1
Lightly grease a 9-inch tart pan with nonstick spray and place on a baking sheet. Make sure you have room in your freezer and fridge to place the tart pan later.
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2
In the bowl of an electric mixer fitted with the paddle attachment, cream the butter and brown sugar until light and fluffy, 3 to 4 minutes. Add the vanilla and egg yolk and mix to combine.
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3
Add the flour and salt and mix until the dough comes together and is uniform. The mixture should look like a stiff chocolate chip cookie dough - if it seems dry or crumbly, add a little milk (1 tablespoon at a time) until it comes together. Add the chocolate chunks and mix to combine.
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4
Press the dough into the prepared tart pan into an even layer - take special care to make sure the sides of the tart dough and the corner (where the sides meet the base) aren't too thick. Using a small measuring cup can help you get into those corners and ensure it's even.
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5
Place the tart pan into the freezer while you preheat the oven to 350u00b0F.
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6
Press the tines of a fork all over the chilled dough to dock it. Bake until the crust is lightly golden brown and fully baked, 20 to 24 minutes. Cool completely.
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7
When the crust is cool, make the filling. Place the cool water in a small bowl, and sprinkle the gelatin over it. Let it sit for 5 minutes.
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8
Heat 1 cup of the heavy cream, sugar, and the vanilla bean and scrapings in a medium pot, stirring until the sugar is dissolved, 1 to 2 minutes. Add the bloomed gelatin and heat until the mixture melts completely, about 1 minute.
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9
Place the hot liquid into a large vessel with a pour spout (such as a 4 cup liquid measuring cup), and stir in the remaining 1/4 cup cream and the milk, stirring well to combine. Remove the vanilla bean (if using vanilla extract instead of the bean, stir it in now).
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10
Pour the filling into the cooled crust, and gently transfer to the refrigerator. Chill until the filling is totally set, at least 1 hour, and up to 8 hours.
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11
The tart is now ready to serve, or you can add the optional topping. In an electric mixer fitted with the whip attachment, whip the cream, powdered sugar, and vanilla to medium peaks. Spread the cream on top of the tart, and decorate with mini chocolate chip cookies.
