Make the almond tart dough: In a small bowl, lightly whisk the egg and set it aside. Put the almonds and sugar in the bowl of a food processor, and pulse until the almonds are finely ground. Add flour and salt and pulse again just until mixed. Add the butter and pulse until sandy (about 6 to 10 quick pulses). Pour in the egg and pulse just until the dough begins to cohere into a ball. Form the dough into a disk, wrap it tightly in plastic wrap, and refrigerate it for at least 1 hour or overnight.
Make the coconut cream filling: Place the white chocolate in a heatproof bowl. In a small saucepan set over medium heat, heat the cream just to boil. Pour it over the white chocolate and let stand for 30 seconds. Slowly, starting in the center of the bowl, whisk the cream and white chocolate until smooth. Cover and refrigerate this ganache for 4 hours or overnight before proceeding (the coconut and rum will be added later).
Place the tart pans in the freezer for 30 minutes. Preheat the oven to 375 degrees F. Line the tart crusts with aluminum foil, and fill each one three-quarters full with pie weights or dried beans. Bake them for 15 minutes, then remove the foil and weights and bake for another 10 minutes or until lightly browned.
Make the coconut cream filling: Meanwhile, in the bowl of a standing mixer fitted with the whisk attachment, beat the white chocolate ganache at medium speed until soft peaks form. Do not over whip. Gently fold in the coconut and the rum. Divide the filling evenly among the cooled tart shells and place in the refrigerator while you make the chocolate glaze.
Make the chocolate glaze: Place the milk and dark chocolate in a medium heatproof bowl. In a saucepan, heat the heavy cream until it is just about to boil. Pour it over the chocolates and whisk to combine. Let the mixture set for about 10 minutes. Remove tarts from the refrigerator and spoon the glaze evenly over each one. Top tart with one almond and refrigerate again until glaze sets up, about 10 minutes.