Prepare one batch of home-made caramel sauce according to instructions; video recipe link above. The sauce can be made up to a week in advance and stored in the refrigerator. If short on time, use store-bought caramel sauce.
Preheat oven to 375F (190C) and prepare the crust. Place graham crackers and almonds into a food processor and pulse into fine crumbs. Add the melted butter and pulse again until crumbs are well coated. Transfer the crumbs into a 9-inch (23-cm) tart pan. Using a spoon or your hands, press the crumbs into the bottom and sides of the tin to form a firm and even crust. Bake crust in preheated oven for 12 to 13 minutes, just until golden. Remove and cool on wire rack.
Next, prepare the chocolate custard filling. In a medium-sized mixing bowl, whisk together the egg yolk and sugar for about 1 minute, until the mixture is pale and ribbons off whisk. In a small ramekin, combine the cornstarch and water to form a slurry, then whisk into egg yolk mixture.
In a separate sauce pan, combine the milk and flour. Heat over medium heat, stirring, until the milk is steaming hot but not boiling. Temper the hot milk slowly into the egg yolk mixture, adding the milk in small increments and mixing well after each addition. Pour the resulting mixture back into the sauce pan. Cook over medium heat, stirring constantly, for about 5 minutes or until the mixture thickens into a custard.
Remove the custard from heat and add the chocolate and liqueur (optional). Whisk in the chocolate until it's melted and smooth. Transfer the custard over prepared crust and use an off-set spatula to spread it evenly to the edges. Place the tart into refrigerator to chill for at least 20 minutes.
Meanwhile, prepare the meringue. Place the egg whites into a stand mixer bowl. Make sure bowl is very clean and free of any oil residue. Whisk the eggs for a few minutes until soft peaks form. Combine the water and sugar in a small saucepan and attach a candy thermometer to the side. Cook over medium-high heat for 5 to 6 minutes, until the thermometer reaches 238F.
Pour the hot syrup into the egg whites with the mixer running on medium speed. Once all the syrup is added, turn mixer up to high speed and whisk for 5 to 8 minutes, until meringue is thick and glossy.
Assemble the tart: spread the caramel sauce over the chilled chocolate custard. To spread the caramel evenly, transfer it into a pastry bag and pipe over the custard. Top the caramel with sliced strawberries, then scoop the meringue over the top. Use a kitchen torch to caramelize the meringue. Keep tart refrigerated if not serving immediately.