Step 1: Prepare the Choux Pastry Shells

1. Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

2. In a saucepan, combine the water, milk, butter, sugar, and salt. Bring to a boil over medium heat.

3. Once the butter has melted and the mixture is boiling, add the flour all at once. Stir vigorously with a wooden spoon until the mixture forms a ball and pulls away from the sides of the pan.

4. Remove the mixture from the heat and let it cool for about 3-5 minutes.

5. Add eggs one at a time, beating well after each addition. The dough should become smooth and pipeable.

6. Transfer the dough into a piping bag and pipe 4-5 inch long logs onto the prepared baking sheet.

7. Bake at 400°F (200°C) for 15 minutes, then reduce the temperature to 350°F (175°C) and bake for an additional 20-25 minutes, until golden brown and crisp.

8. Let the choux shells cool completely on a wire rack.

Step 2: Prepare the Red Bean (Anko) Filling

1. In a mixing bowl, combine the sweetened red bean paste (anko) with heavy cream if you want a smoother texture.

2. Mix until the mixture becomes smooth and pipeable. Set aside.

Step 3: Prepare the Matcha Pastry Cream

1. In a saucepan, heat the milk over medium heat until it begins to steam, but do not let it boil.

2. In a separate bowl, whisk together the egg yolks, sugar, and cornstarch until smooth and pale.

3. Gradually pour the hot milk into the egg mixture, whisking constantly to temper the yolks.

4. Pour the mixture back into the saucepan and cook over medium heat, whisking constantly until the cream thickens and begins to bubble.

5. Once thickened, remove from heat and whisk in the butter and matcha powder.

6. Cover the pastry cream with plastic wrap, making sure the wrap touches the surface to prevent a skin from forming. Chill in the refrigerator for at least an hour.

Step 4: Prepare the Matcha Glaze

1. In a bowl, whisk together the powdered sugar and matcha powder.

2. Add 1–2 tablespoons of milk or water and whisk until the glaze is smooth and glossy.

Step 5: Assemble the Matcha & Red Bean Éclairs

1. Slice each choux pastry shell in half lengthwise or poke three holes in the bottom for filling.

2. Pipe a layer of red bean filling into each shell, followed by a generous layer of matcha pastry cream.

3. Dip the tops of the éclairs into the matcha glaze and allow them to set.

4. (Optional) Garnish with gold flakes, roasted sesame seeds, or candied azuki beans for an extra touch of elegance.