How to Make It
Preheat the oven to 400° and line a large baking sheet with parchment paper. In a medium saucepan, bring the water, salt, sugar and butter to a boil. Add the flour all at once, remove from the heat and stir until a smooth ball forms. Transfer the dough to a bowl and let cool for 1 minute. Using an electric mixer, beat in the eggs one at a time, beating well between additions, until smooth.
Scoop the dough onto the baking sheet in 8 mounds. Using a lightly moistened finger, smooth the tops. Bake for 10 minutes, then lower the heat to 250° and bake for 15 minutes longer, until the puffs are lightly golden. Let cool completely.
In a saucepan, bring the milk, salt, vanilla bean and seeds to a boil. In a bowl, whisk the sugar, cornstarch and eggs. Whisk in 1/2 cup of the hot milk. Whisk the mixture into the remaining milk in the saucepan and cook over moderate heat, stirring constantly, until very thick and bubbling, about 4 minutes. Off the heat, whisk in the butter. Strain the pastry cream into a bowl, place a sheet of plastic wrap directly onto the surface and refrigerate until chilled, about 1 hour.
In a small saucepan, combine the strawberry preserves with the water and bring to a simmer. Whisk vigorously to break up the fruit. Strain the mixture into a medium bowl. Add the confectioners' sugar and whisk until smooth.
In a medium bowl, toss the strawberries with the sugar, vanilla seeds and tarragon.
Split the cream puffs horizontally and gently pull out any soft dough from the centers. Spoon the pastry cream into the puffs, top with some strawberry slices and replace the tops of the puffs. Spoon some of the glaze on top and refrigerate until set, about 10 minutes. Serve.