Instructions

1. Make the choux pastry: Position a rack in the center of the oven and preheat to 425°F. Line two baking sheets with parchment.
2. In a medium pot over medium-high heat, bring the milk, butter, kosher salt, and ⅔ cup water to a boil. Using a wooden spoon or stiff silicone spatula, gradually add the flour and stir to work into a paste. Turn the heat to medium-low and cook, stirring continuously, until a film forms on the bottom of the pot and the dough forms a ball, 3–4 minutes. Remove from the heat.
3. To a stand mixer fitted with a paddle attachment, transfer the dough and mix on low speed until cooled slightly, about 2 minutes. Add the eggs one at a time, mixing until each egg is fully incorporated before adding the next, 1–2 minutes. Stop and scrape down the sides of the bowl occasionally. Mix in the quatre-épices until combined.
4. Transfer the choux pastry to a piping bag fitted with ⅜-inch plain metal tip. Onto the lined baking sheets, pipe 1½-inch lengths of pastry in rows, leaving at least ½ inch between each. With a wet finger, smooth any uneven ends left from the piping tip.
5. Bake for 5 minutes, then turn the oven temperature to 350°F and continue baking until the éclairs are golden brown and puffed, 15–20 minutes more. Transfer to a wire rack to cool completely. 
6. Make the camembert cream: To a small pot, add the oil and turn the heat to low. To a food processor, add the eggs. When the oil temperature reaches 160°F on an instant-read thermometer, turn on the food processor and slowly stream in the oil until the mixture is the consistency of mayonnaise. Stop and scrape down the sides with a spatula. Add half of the crème fraîche and the xanthan gum and process until incorporated. Add the remaining crème fraîche and process to combine. Add the camembert and process until fully smooth and incorporated, about 2 minutes. Season to taste with kosher salt, then transfer to a piping bag fitted with a thin tip and set aside at room temperature.
7. Make the toasted honey and white chocolate ganache: To a medium heatproof bowl, add the white chocolate. In a small pot over medium-low heat, stir together the cream and kosher salt and bring just to a simmer. Meanwhile, in a deep pot over high heat, cook the honey, stirring occasionally, until it turns a dark caramel color, 5–7 minutes. Add the hot cream mixture to the honey slowly (it will foam and bubble), stir well to incorporate, then immediately pour the honey caramel over the white chocolate. Set aside to allow the chocolate to melt for a minute or two, then whisk well until smooth and fully combined. Whisk in the butter until fully incorporated, then set the ganache aside until cooled and thickened slightly, 20–25 minutes.
8. To assemble: Using the wide end of a chopstick, poke holes in both ends of the éclairs, then pipe the cream into both ends. Dip the tops of the éclairs in the ganache, garnish with flaky salt, lemon zest, and nuts (if desired), then set aside at room temperature until set. Serve at room temperature.