In a medium saucepan, bring milk and ½ cup heavy cream to a simmer over medium-high heat.

Remove from heat; add tea leaves and steep for 5 minutes. Strain; discard tea leaves. Set infusion aside. Reserve remaining ¼ cup cream for assembly.

In a clean, medium saucepan, whisk together egg yolks, sugar, cornstarch, and salt until smooth. While whisking, slowly add the tea-infused milk mixture until fully incorporated.

Add the butter and bring to a simmer over medium heat.

Reduce heat to medium-low and cook, stirring constantly, ensuring to clear the edges of the pan until the mixture begins to thicken, up to 15 minutes. Alternate between a rubber spatula and whisk while stirring for best results.

Let the mixture slowly come to a boil and cook for one additional minute.

Transfer the custard to a bowl and place plastic wrap directly onto the surface of the custard.

Refrigerate until chilled, 1½ hours minimum.

Preheat oven to 450°F.

In a medium saucepan, bring the butter, sugar, salt, and water to a simmer over medium heat.

As soon as it comes to a boil add the flour, stirring constantly with a wooden spoon until a dough ball forms and pulls away from the sides of the pan, about one minute.

Remove the pan from the heat and let the mixture cool for 3 to 4 minutes, stirring occasionally.

Add the eggs, one at a time, whisking vigorously between each addition with a wooden spoon. The dough will break apart and slide around in the pot before it comes back together. Whisk until it regains a smooth consistency.

Transfer the dough to a piping bag fitted with a large, round tip (or a one-gallon zip-top bag and snip one corner).

Line two baking sheets with parchment paper. Pipe the dough into 5-inch x ¾-inch lengths and space about three inches apart. Smooth out any peaks or points with a damp finger.

Bake until puffed and golden brown, about 45 to 50 minutes, rotating the sheets halfway through. They should be very light and crisp. Remove from oven and turn the oven off.

Poke one end of each pastry with a toothpick to allow some steam to escape. Return pastry to oven to dry out, about 15 minutes. (Prop oven door open with a wooden spoon.) Transfer baking sheet to a wire rack to cool completely.

In a small saucepan, bring ¼ cup of heavy cream and salt to a simmer over medium heat.

Remove from heat; add dark chocolate and corn syrup. Let the mixture stand for one minute, then whisk until smooth.

To finish the custard, whisk the remaining ¼ cup of heavy cream into the cooled custard to loosen.

Transfer the custard to a pastry bag fitted with a fluted tip (or a one-gallon, zip-top bag and snip one corner) for piping.

Slice the top-third off each éclair and fill the pastry base with custard. Dip the tops of the pastry in the icing to coat and set them on top of the custard-filled bases.