Heat the oven to 180 C / 355 F. Lightly grease a 12-cup mini tart pan or 12 individual 7 cm tart molds.

Add the flour, powdered sugar, and salt to a mixing bowl. Add the cold cubed butter and rub it in with your fingertips until the mixture resembles coarse breadcrumbs with some pea-sized pieces remaining.

Add the egg yolk and cold water. Mix with a fork until the dough just comes together. Do not overwork it.

Shape the dough into a disc, wrap it, and refrigerate for 30 minutes.

Divide the chilled dough into 12 equal pieces. Press each piece evenly into a tart mold, working it up the sides to a thin, uniform thickness.

Line each shell with a small square of parchment paper and fill with pie weights or dried beans. Blind-bake for 10 minutes.

Remove the weights and parchment. Return the shells to the oven and bake for a further 5 minutes until the base is golden and dry. Cool completely on a wire rack before filling.

In a chilled mixing bowl, whip the heavy cream with a hand mixer on medium-high speed until it holds soft peaks. Set aside.

In a separate bowl, beat the mascarpone, powdered sugar, and vanilla extract until smooth and creamy, about 1 minute.

Pour in the cooled espresso and beat on low speed until just combined and the color is even throughout.

Fold the whipped cream into the mascarpone mixture in two additions using a spatula, keeping the mixture light and airy.

Transfer the filling to a piping bag fitted with a star tip. Refrigerate for 10 minutes if the cream feels too soft to pipe.

Pipe the espresso cream into each cooled tart shell in a swirl motion, starting from the outside edge and working inward.

Dust cocoa powder lightly over the tarts through a fine-mesh sieve held about 15 cm above the surface.

Place one chocolate-covered espresso bean in the center of each tart if using. Serve immediately or refrigerate until needed.