Prepare the Pate a Choux.
Preheat oven to 375 degrees. Make an egg wash by whisking together egg with 1 tablespoon water in a small bowl. Set aside.
Line two large baking sheets with parchment paper. Transfer Pate a Choux to a pastry bag fitted with a 5/8-inch plain tip. Pipe dough into 2-inch rounds about 1 inch apart. Gently smooth the pointed peaks with a moistened finger, rounding tops to ensure even rising. Brush tops with egg wash. Bake until puffed and golden brown, about 25 minutes. The cream puffs should feel light and airy. Remove puffs from oven and transfer sheets to wire racks to cool completely.
Make the pastry cream: Scrape seeds from the vanilla bean. In a heavy saucepan, combine milk, vanilla bean and seeds, and 1/2 cup sugar. Scald the mixture and immediately remove from heat.
Beat egg yolks with remaining 2 tablespoons sugar until thick. Sprinkle in flour and cornstarch and continue beating until mixed.
Beat half of the hot milk into yolk mixture. Return this to the remaining hot milk and bring to a boil quickly, whisking very fast to prevent scorching. Remove from heat and strain into a bowl to cool. Stir in butter. Cover with plastic wrap, pressing directly on the surface of the pastry cream to prevent a skin from forming. Transfer to the refrigerator to chill completely. Immediately before using, gently fold in softly whipped cream with a spatula.
Transfer pastry cream to a piping bag fitted with an 1/8-inch plain tip. Insert the tip into the opening of each pastry, and pipe to fill with pastry cream.
Make the maple-espresso glaze: In a small bowl, whisk to combine heavy cream, espresso powder, and maple syrup. Add confectioners' sugar and whisk until smooth, thinning with additional heavy cream if necessary.
Dip the top of each cream puff into the maple-espresso glaze; let excess drip off, and place, coated side up, on a wire rack set over a rimmed baking sheet. Refrigerate cream puffs in a single layer until glaze is set, about 10 minutes, and serve.