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Prepare the pastry cream: Cut vanilla bean in half crosswise, then cut a slit lengthwise down each half. Use the edge of the knife to scrape out all the seeds. Discard the pods or reserve for another use.
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Combine sugar, cornstarch, salt, egg, egg yolks, milk, and vanilla seeds in a saucepan; whisk until well combined.
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Place over medium heat and cook, stirring constantly and scraping the bottom surface of the pan, until thick, about 10 minutes.
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Remove from the heat and whisk to release some steam. Add butter and keep stirring until melted. Pass through a fine sieve to remove any fibrous bits from the vanilla pod. Place plastic wrap directly on the surface of the pastry cream to cover and refrigerate until thoroughly chilled, at least 2 to 3 hours.
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Preheat the oven to 425 degrees F (220 degrees C). Line a baking sheet with a silicone liner (such as Silpat®).
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Combine butter, water, and salt for the pate choux in a saucepan over medium-high heat; bring to a simmer. Add flour and stir with a wooden spoon until a buttery dough forms. Continue to cook and stir until a starchy film forms on the bottom of the pan. Turn off the heat and continue stirring for 1 more minute.
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Transfer to a bowl. Add one egg and mix it in with a little dough. Once that's incorporated, mix it in with the remaining dough. Repeat with the second egg. Continue stirring until you have a very sticky dough. Use a spatula to clean off the whisk if necessary.
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Transfer the dough into a pastry bag and snip off the tip making a ½-inch opening. Pipe two 6-inch heart shapes on the prepared baking sheet. Start by making thin shapes and then pipe extra dough to make them thicker. To fine-tune the hearts, dip your fingers in water and fix any imperfections if desired.
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Bake in the center of the preheated oven until beautifully browned, about 30 minutes. Turn off the heat, leave the pastries in the oven, and prop the oven door open with a wooden spoon. Let sit until crispy and dried out, about 1 hour.
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Use a serrated knife to slice the hearts in half horizontally.
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Remove pastry cream from the refrigerator and transfer to a pastry bag. Generously pipe cream into the bottom half of each heart, then place the top halves on the cream.
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Heat cream in a saucepan until simmering.
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Place chocolate chips in a small bowl and pour hot cream over top. Let sit for 2 to 3 minutes, then whisk until chocolate has melted and ganache is thick and shiny. Let cool for about 5 minutes.
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Spoon ganache on top of each heart. Reserve any remaining ganache for another use. Refrigerate éclairs until the ganache is firm, about 15 minutes.
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Place éclairs on serving plates. Fill the center of each heart with raspberries and sift cocoa powder over top. Sift powdered sugar over just the raspberries and serve. (Each éclair is enough for two people.)
