In a food processor, pulse the flour with the icing sugar and the salt. Add the chilled butter and pulse again until the mixture becomes coarse. Then, in a small bowl, whisk the egg yolk with the ice water. With the machine on, slowly incorporate the egg yolk mixture and process until the dough comes together.
Bring it to a work surface and knead it three or four times. Divide the dough in half and pat it into two discs. Wrap them in plastic wrap and refrigerate for a minimum of 30 minutes.
Meanwhile, prepare the pans: butter the mini spring forms and cut out discs out of parchment paper, with a diameter 2 inches larger than the diameter of the spring forms. Ease the discs into the spring forms (I like to cut 1 inch long slits pointing at the center to make this work easier). If you’d rather not use parchment paper, simply butter the mini pans.
Preheat the oven to 375°F. Let the dough stand at room temperature for about 10 minutes. Then, on a lightly floured work surface, roll out one disc of dough to a thickness of about 1/4 inch. Cut out six disks the diameter of the mini spring forms (you can use the base of the mini spring form to mark them on the dough). Ease the discs onto the base of the springform.
Roll out the second disc of dough and cut strips with a width the height of the spring forms. Ease them into the side wall of the spring forms.
Out of wax paper or parchment paper (I used wax paper) cut out six disks the diameter of the springform pan. Place them on top of the dough and fill with pie weights or dry beans. Bake the shells for about 20 minutes, checking at the 15 minute mark. The shells should be just set and slightly dry. Transfer to a rack and let cool.
For the filling:
Preheat the oven to 325°F.
In a large mixing bowl, whisk the eggs with the sugar and lemon zest until combined. Add the lemon juice and heavy cream and stir until combined. Incorporate the shredded coconut.
When the tart shells are completely cold, divide the filling into the tarts. Place in the oven and bake them for about 35 minutes, or until the filling is set and the tops are slightly golden around the edges. Transfer to a rack to cool down.
For the passion fruit frosting:
Combine the mascarpone cheese with the cream and the icing sugar. Beat at medium speed until the frosting begins to thicken. Add 1/3 cup passion fruit pulp and beat again. Refrigerate for about one hour.
When the tarts are completely cooled down, or just before serving, top the tarts with a generous dollop of the frosting. Use the back of a spoon to make a well in the center and fill it with 1 tablespoon of the passion fruit pulp
Notes
The shells can be made one day in advance and stored at room temperature
The tarts can be kept at room temperature for about two days, but make sure the frosting stays refrigerated.
Instead of passion fruit I used passion fruit puree found at Costco