Whisk the flour, sugar, and salt in a mixing bowl. Rub in the cold butter with your fingertips until the mix looks like pea-size crumbs with a few flat flakes. Sprinkle over 80 ml ice water and toss with a fork. Add up to 10 ml more only if the crumbs won't hold when squeezed. Press into a disk, wrap, and chill for 30 minutes.

While the dough chills, combine the coconut, brown sugar, water, and ginger in a 20 cm / 8-inch heavy-bottomed saucepan (2-quart / 1.9 L). Cook over medium-low heat, stirring every minute or two, for 12 to 14 minutes. It's ready when the liquid is gone, the mixture looks glossy, and a spoon dragged across the pan leaves a clear trail. Stir in the nutmeg, vanilla, and salt and cook for 1 minute more.

Scrape the filling into a bowl and let it cool to room temperature, about 15 minutes. Warm filling softens the dough, so don't rush this.

Heat the oven to 190 C / 375 F and line a 33 x 46 cm / 13 x 18-inch sheet pan with parchment. Roll the chilled dough on a floured surface to 3 mm thick. Cut 9 cm / 3.5-inch rounds, rerolling the scraps once, to get 12 rounds.

Set the rounds on the sheet pan with space between them. Spoon 1 heaped tablespoon (about 27 g) of filling into the center of each, leaving a bare border of about 2 cm. Pinch the border at 6 evenly spaced points, pulling the dough up and slightly inward into a standing wall. Press each seam between pinches firmly so the walls don't slump.

Bake for 22 to 25 minutes, rotating the pan halfway through, until the pinched edges are golden and the filling looks dark and glossy.

Transfer the tarts to a wire rack and cool for at least 10 minutes before eating. The filling is very hot straight from the oven. Serve warm or at room temperature.