Mix the Pastry Dough: In a large bowl, mix the flour, salt, and sugar. Add the lard and cut it into the flour with a dough blender (or two butter knives) until it resembles coarse crumbs. Add the ice water 2 Tablespoons at a time, kneading with your hands until a total of 9 Tablespoons is incorporated. Shape the dough into a ball (it should not be sticky). Wrap tightly in plastic wrap and refrigerate for at least 2 hours (overnight is best).
Laminate the Pastry: On a lightly floured surface, roll the cold dough into an 8x15-inch rectangle. Place 4 or 5 slices of the cold butter in the center. Fold the bottom third of the dough up over the butter. Place the remaining butter slices on top of the fold, then fold the top third of the dough down. Dust with flour and roll the dough out into an 8x15-inch rectangle again. Fold the dough in thirds one more time. Roll the dough to a final 8x15-inch rectangle with a 1 cm thickness. (Refrigerate for 30 minutes if the dough feels soft).
Cut the Shells: Using a 4-inch round cookie cutter, press straight down into the dough. DO NOT twist the cutter! Lift the cut-out disc and press it into a 3-inch egg tart mould using a tart tamper or your fingers. Repeat for all moulds. Place the filled moulds on a baking sheet and refrigerate your shells while you work on the next step.
Make the Custard: In a small saucepan over medium heat, stir the evaporated milk, water, white sugar, vanilla sugar, and salt. Warm for 5 minutes just until the sugar dissolves (do not boil). Let cool for 10 minutes (this step is important to prevent the eggs from overcooking). In a large bowl, whisk the whole eggs and egg yolks. Slowly whisk the cooled milk mixture into the eggs. Pour the custard through a mesh strainer into a large measuring cup to remove air bubbles. Preheat the oven to 350°F (177°C).
Make the Plum Roses: Stack 2 thin plum slices parallel to each other and roll them tightly together. Insert 2 toothpicks in an "X" shape through the bottom to hold the rose together. Repeat to make 24 roses.
Assemble and Bake: Place a plum rose into the center of each tart mould, lightly pressing the toothpicks into the pastry base. Slowly pour the egg custard into the shells, filling them only halfway. (Leave 1 cm of pastry overhang as it will shrink). Repeat this until all moulds are decorated and filled. Carefully, transfer the tray to the middle oven rack and bake for 26 minutes. The egg center should be a little jiggly.
Cool and Serve: Remove from the oven and let cool for 10 minutes. Carefully remove all wooden toothpicks from each tart. Slide the egg tarts out of the moulds and onto a wire rack. You can place each egg tart into a cupcake liner for a little decorative 'oomph'. Serve warm or at room temperature. Dust with icing sugar before serving if you prefer!