For the crust, preheat oven to 375°F. Butter a 9-inch square cake pan. Line with parchment paper with about 2-inch overhand on each side. Butter the parchment paper as well. Set aside. Place butter, sugar and salt in the bowl of a food processor. Blend until uniformly mixed. Add flour all at once. Pulse until the mixture has the consistency of wet sand. Dump the mixture into the cake pan and press evenly into the corners of the pan. Bake for 15 to 18 minutes until golden brown. The crust will seem fairly soft and underdone. Don’t worry. It will get baked again. Set aside and let cool. For the filling, lower the oven's heat to 350°F. Add both milks and vanilla extract into a heavy-bottomed saucepan. Cook over medium low heat, stirring constantly for 45 minutes to 1 hour. You can step away from the stove for a couple of minutes at a time in the beginning, but as the mixture thickens, you will need to be at the stove constantly stirring to avoid burning. The mixture is ready when it's beige in color and you can see the bottom of the pan when you draw your spoon across it. At this point, immediately remove the saucepan from the heat. Beat in the egg yolks followed by the pisco or brandy. Using a rubber spatula, transfer the mixture on top of the cooled shortbread crust that you have set aside. Bake for 15 to 20 minutes or until the mixture is firm and lightly golden brown on top. Set aside and allow to come completely to room temperature. You can also place it in the refrigerator, covered, for up to 2 days until you're ready to top it with Italian meringue and serve. For the Italian meringue, place the sugar and port in a small saucepan. Boil over medium high heat until sugar completely dissolves. Turn off burner to keep the syrup warm. Place the egg whites and cream of tartar in a stand mixer or large mixing bowl. With the whisk attachment or with a hand mixer, beat the egg whites until they form stiff peaks. With the the mixer running, slowly pour in the warm syrup in a thin stream. You will see the egg whites get shiny and turn a light lavender color. Keep beating and pouring in the syrup until it is all incorporated into the meringue. Transfer the Italian meringue to a piping bag fitted with a fluted tip. You can store the meringue for up to a day until you are ready to assemble the dessert. To assemble: Using the parchment overhang, carefully remove the bars from the baking pan and transfer onto a large cutting board. Slice off the browned sides (these are unattractive and can taste bitter). Cut into even squares. If you want bigger squares, divide the tart into 9 even pieces. For smaller bites, you can divide it into 16 pieces. Artfully pipe the Italian meringue on top of each square. Traditionally, there is up to 2 times as much meringue as there is filling. However, you can add as much or as little as you’d like. Generously dust with ground cinnamon. You can store the squares in the refrigerator for up to a day until you're ready to serve them.