Make the cold tea infusion for the topping early in the day or a day ahead. Stir the cream and tea leaves together in a bowl. Cover and chill for 8 to 12 hours. Even if you are not using the cream right away, strain the tea out and discard it after 12 hours. Refrigerate the cream until needed.

To make the crust, position a rack in the lower third of the oven and preheat the oven to 350°F.

In a medium bowl, combine the melted butter with the sugar, vanilla, and salt. Add the flour and mix just until well blended. If the dough seems too soft, let it stand for 5 minutes to firm up.

Press the dough evenly across the bottom and up the sides of the tart pan; to avoid ending up with extra-thick edges, press the dough squarely into the corners of the pan. Place the pan on a cookie sheet and bake until the crust is a deep golden brown, 20 to 25 minutes; press it down with the back of a spoon or prick it with a fork if it bubbles up. Let cool completely on a rack before making the filling.

To make the filling, place the chocolate, butter, and citrus zest in a small heatproof bowl (stainless steel is best), set it in a wide skillet of not-quite-simmering water, and stir frequently until the chocolate and butter are completely melted and smooth. Remove the bowl, set a fine strainer over it, and set aside. Leave the skillet over low heat.

Place the egg yolk in a small bowl and gradually whisk in the boiling water. Place the egg bowl in the skillet and stir constantly with a silicone spatula, sweeping the bottom of the bowl to prevent the egg from cooking, until the mixture registers 160°F on the instant-read thermometer. Remove the bowl from the skillet and immediately scrape the yolk mixture into the strainer set over the bowl of chocolate. Stir gently, without whisking or beating, just until the egg is incorporated completely into the chocolate and the mixture is smooth (except for the bits of zest).

Pour the filling into the cooled tart shell and spread it evenly. Place in a covered container (or cover with an inverted bowl if you don’t have an appropriate container), and refrigerate at least until the filling is set (3 to 4 hours), or up to 2 days.

About 30 minutes before serving, remove the tart from the refrigerator, to soften the filling and bring back its sheen. Remove the pan sides, and place the tart on a platter.

Whip the jasmine-infused cream until thickened. Add the sugar (you want the cream only gently sweetened so that the sweetness doesn’t overpower the subtle flavor of the jasmine and the tea) and whip until it holds a soft shape, or a little stiffer if you plan to pipe the cream.

Using a pastry bag, decorate the tart with the jasmine cream or serve plain wedges with dollops of cream. If desired, add the citrus zest garnish or candied peel.