Step 1Scrape the seeds from the split vanilla bean into milk in a saucepan. Heat the milk just to a simmer.
Step 2Whisk the sugar into the egg yolks and beat until pale yellow and a thick ribbon consistency. Whisk in the flour.
Step 3Add a little of the hot milk to the egg mixture to temper, then stir in remaining hot milk.
Step 4Strain the hot milk mixture back into a saucepan and return to heat. Heat and stir to boiling. Reduce the heat and simmer about 1 minute or until the pastry cream is shiny and thick.
Step 5Transfer the hot pastry cream to a mixing bowl. Beat on medium speed, adding 1 tablespoon cold butter bit by bit until the custard is cooled. Cover tightly and chill until cold.
Step 1Heat the oven to 400 degrees. Bring 1 cup plus 1 1/2 tablespoons water, the salt, sugar and butter to a boil over medium high heat.
Step 2Remove from heat and stir the flour in all at once. Mix well and put back on the stove over high heat. Cook and stir to dry out the paste, 3 to 4 minutes.
Step 3Transfer the paste to a bowl and let it cool at least 5 minutes.
Step 4Beat in the eggs one at a time, beating well after each egg is added so it is completely mixed in.
Step 5Pipe 5- to 6-inch lengths of paste, using a half-inch tip, onto parchment-lined sheet trays. Bake about 30 minutes, until golden brown and crisp.
Step 1When ready to assemble, combine the creme fraiche and sugar. With the tip of a knife, scrape out the seeds from the vanilla into the creme fraiche. Beat to firm peaks, 2 to 2 1/2 minutes.
Step 2Slice one-third horizontally off the top of each choux pastry. Set aside the top parts. Pipe the pastry cream into the bottom of the shells using a small, plain tip. Then, pipe in the Chantilly cream using a medium French (fluted) tip.
Step 3Cut thin strips from the pastry tops and place one strip on top of the Chantilly cream on each filled pastry shell.