Prepare the Éclairs: Line two baking sheets with parchment paper. Transfer the pâte à choux into a piping bag fitted with a ½-inch round tip. Pipe 4-inch lines onto the parchment, spacing them evenly. Smooth any peaks with a wet fingertip. Let the piped dough rest at room temperature for 15-30 minutes.

Bake: Preheat the oven to 375°F (190°C). Brush the éclairs with egg wash. Bake for 35-40 minutes until golden and crisp. Immediately after removing from the oven, poke a small hole in each éclair to release steam. Allow to cool completely.

Prepare the Filling: In a saucepan, bring the strawberry jelly to a boil, then simmer until reduced to about ⅔ cup. Let cool, then transfer to a piping bag. In a bowl, rub the granulated sugar with the vanilla bean seeds. In a mixer, whip the heavy cream with the vanilla sugar to soft peaks. Add mascarpone and salt; whip to medium-stiff peaks. Transfer to another piping bag fitted with your preferred tip.

Make the Glaze: Pulse freeze-dried strawberries in a food processor until powdered. Reserve 1-2 tablespoons for garnish. Combine the remaining powder with powdered sugar. Sift into a bowl and whisk in ¼ cup heavy cream, adding more as needed for a thick but pourable consistency.

Assemble: Slice each éclair horizontally. Pipe a layer of reduced strawberry jelly onto the bottom halves. Pipe the mascarpone cream over the jelly. Place the top halves back on. Spoon the strawberry glaze over the top of each éclair, allowing it to drip slightly down the sides. Sprinkle with reserved strawberry powder.