Special equipment: a pastry bag fitted with a large tip (No.808 round or Nos.866, 867 or 868 star); a pastry bag fitted with a medium round tip
For the choux pastry: Preheat the oven to 375 degrees F. In a large saucepot over medium-high heat, bring the butter, salt and water to a boil. Using a wooden spoon, add the flour in thirds, stirring it in as fast as possible. Smash any lumps against the side of the pot.
Cook the mixture until the dough forms a ball that pulls away from the sides of the pot, about 2 minutes.
Add the dough to the bowl of a stand mixer and let it sit and cool for 5 minutes. Beat on low for 1 minute to release steam. Add the eggs, one at a time, until the dough is smooth and pipeable yet still holds its shape.
Add the dough to a pastry bag fitted with a large tip. Place 4 tiny dabs of dough in the corners of a large baking sheet, then tack down a piece of parchment on top. Pipe the dough into 5-inch lines about 2 inches apart from each other on the prepared baking sheet. Bake, rotating once halfway through, until deep golden brown and dry in the centers, 20 to 25 minutes. Let cool.
For the whipped cream: In a stand mixer fitted with a paddle attachment, beat the cream cheese with the sugar and vanilla seeds until smooth. Add the heavy cream and continue to beat until medium peaks form. Transfer to a pastry bag fitted with a medium round tip.
For the chocolate glaze: Meanwhile, melt the chocolate over a double boiler. Remove from the heat and stir in the butter until completely melted. Whisk together the corn syrup and cocoa powder in a small bowl, then whisk into the chocolate mixture. Set aside until ready to use, but don't refrigerate.
For the poured fondant glaze: Combine the confectioners' sugar, corn syrup and water in a bowl set over a double boiler. Heat, whisking, until smooth and uniform. Turn the heat off and let sit over the water bath until ready to use. Whisk again right before using.
Insert the tip of the pastry bag with the whipped cream into the ends or bottoms of the eclairs to fill them. Dip filled eclairs into the glazes and place on a rack to set.