Make the crust. In a medium-size mixing bowl, cream together the sugar and shortening. In a small mixing bowl, combine the milk, egg, and vanilla and mix well. Add the milk mixture to the shortening mixture and blend well. Combine the flour and baking powder in a medium-size mixing bowl. Then add the shortening mixture, about 1/4 cup at a time, to the dry mixture, blending well between each addition. The dough should come away from the sides of the bowl. Form the dough into a smooth ball, wrap it in plastic wrap, and chill for 30 minutes.
Preheat the oven to 350°F.
Lightly dust a work surface with flour. Divide the dough in half. Gently pat one half of the dough out into a disk. Roll it out into a 12-inch round about 1/4 inch thick. Cut out six 5-inch rounds and line each of six 4-inch round tart pans with a round of dough, pressing it into the bottom and up the side with your fingers. Repeat the process with the remaining ball of dough. With the tines of a fork, randomly prick the dough all over. Put the tart shells on a baking sheet and bake until lightly golden, 12 to 14 minutes. Remove from the oven, then transfer to a wire rack to let cool completely.
Make the filling. In a medium-size nonreactive saucepan over medium heat, combine 2 1/2 cups of the milk and the sugar. Bring to a gentle boil, stirring to dissolve the sugar. Meanwhile, in a medium-size mixing bowl, combine the egg yolks, cornstarch, and the remaining 1/2 cup milk. Whisk until smooth.
Add 1 cup of the hot milk mixture to the egg mixture, whisking to blend. Pour the mixture into the saucepan and cook, stirring constantly, until it thickens, about 4 minutes.
Remove from the heat and pour into a large mixing bowl. Add the vanilla, butter, and coconut. Mix well. Press a piece of plastic wrap down against the surface to prevent a skin from forming. Let cool completely.
Spoon an equal amount of the filling into each tart shell, cover loosely with plastic wrap, and refrigerate for at least 2 hours before serving.
Preheat the oven to 400°F.
Spread the coconut on a baking sheet and bake until just golden, 4 to 6 minutes. Remove from the oven and let cool slightly.
Sprinkle the toasted coconut on the tarts. Serve immediately.
Yield: 12 tarts