Special equipment: 2 4 1/4-inch mini fluted tart tins, a piping bag fitted with a round tip, a toothpick
For the pastry: Add the flour, butter, sugar and salt to a stand mixer fitted with the paddle attachment and mix on low speed until the mixture resembles breadcrumbs and the butter pieces are in small chunks. Add the egg yolk and mix until just combined and beginning to stick together, 15 seconds maximum.
Remove the dough from the mixer and shape it into a disc. Wrap in plastic wrap and chill in the fridge for at least 1 hour and up to 2 days.
Roll out the chilled dough on a floured surface until it is about 1/8 inch thick. Cut out 2 round discs about 5 inches each and lay them over two 4 1/2-inch mini fluted tart tins. Press the dough into the edges, trim off the excess, prick the bottoms in several places with a fork and place in the fridge for 20 minutes.
Preheat the oven to 175 degrees C/350 degrees F. Line the pastry with parchment and fill with dried beans. Bake until the pastry edges are golden brown, about 15 minutes. Remove the parchment and beans, brush the pastry with the egg yolk and bake until the base of the pastry is golden brown, about 5 minutes more. Let cool.
For the meringue kisses: Preheat the oven to 100 degrees C/210 degrees F.
Add the egg whites, vinegar and cream of tartar to a stand mixer fitted with a whisk attachment. Whisk on medium speed until they begin to get frothy, 1 to 2 minutes. As soon as they are frothy, increase the speed to high and slowly add the sugar a teaspoon a time. Keep whisking until you have added all the sugar and the meringue is stiff and glossy, 1 to 2 minutes more.
Add some food coloring to the end of a toothpick and run it along the inside of a piping bag fitted with a round tip.
Place the meringue in the piping bag and pipe small dollops roughly 1/2 inch in diameter onto a baking sheet lined with parchment. Bake the meringues until they are no longer glossy, have a matte finish and feel light and airy, about 40 minutes. Turn the oven off and allow the meringues to cool inside with the door closed for 20 minutes. (Makes 30 to 40 meringues.)
For the chocolate filling: Add the chocolate, butter, cream and sugar to a heat-proof bowl and place it over (but not in) a saucepan pan of simmer water. Gently stir together until melted, 1 to 2 minutes.
Pour the mixture into the cooked pastry shells and chill in the fridge for 40 minutes.
For the assembly: Place 8 to 10 meringues on top of each chocolate tart. Reserve the remaining for another use. Decorate with some sliced raspberries and basil leaves.
If left to chill in the fridge overnight, allow the tarts to sit at room temperature for 20 to 30 minutes before serving.
Recipe courtesy of Topless Baker