Part 1: Making the Sweet Shortcrust Pastry (Pâte Sablée)

1. Combine Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, powdered sugar, and salt until well combined.
2. Cut in the Butter: Add the cold, cubed unsalted butter to the flour mixture. Using a pastry blender, your fingertips, or a food processor (on pulse mode), cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter still visible. This is key for a tender crust.
3. Add Wet Ingredients: In a small bowl, lightly whisk the large egg yolk with 2 tablespoons of ice water. Create a well in the center of the flour-butter mixture and pour in the egg yolk mixture.
4. Form the Dough: Gently mix with a fork or your hands until the dough just starts to come together. Be careful not to overmix. If the dough seems too dry, add the remaining tablespoon of ice water, one teaspoon at a time, until it holds together. The dough should be soft but not sticky.
5. Chill the Dough: Turn the dough out onto a lightly floured surface and gently gather it into a disc. Wrap it tightly in plastic wrap and refrigerate for at least 1 hour (or up to 2 days). This chilling step is crucial; it allows the gluten to relax, making the dough easier to roll, and prevents shrinkage during baking.

Part 2: Baking the Tart Shells

1. Preheat and Prepare Pans: Preheat your oven to 375°F (190°C). Lightly grease a 12-cup standard muffin tin or individual mini tart pans (approximately 3-4 inches in diameter).
2. Roll Out the Dough: On a lightly floured surface, roll out the chilled dough to about ⅛-inch thickness. If the dough is too firm from chilling, let it sit at room temperature for 5-10 minutes.
3. Cut and Fit Dough: Using a round cookie cutter (around 3.5-4 inches, depending on your muffin tin/tart pan size – it should be larger than the top of your tart mold to account for the sides), cut out circles of dough. Gently press each dough circle into the prepared muffin cups or tart pans, ensuring it fits snugly against the bottom and sides. Trim any excess dough from the top edges with a sharp knife or by rolling your rolling pin over the top.
4. Prick and Chill (Again): Prick the bottom of each tart shell a few times with a fork. This prevents the pastry from puffing up too much during baking. Place the muffin tin or tart pans in the freezer for 15-20 minutes (or refrigerator for 30 minutes). This further helps prevent shrinkage.
5. Blind Bake (Optional but Recommended): For an extra crisp crust, line each chilled tart shell with a small piece of parchment paper or a cupcake liner, and fill with pie weights, dried beans, or uncooked rice. Bake for 12-15 minutes.
6. Bake Until Golden: Carefully remove the parchment paper and weights (if used). Continue baking for another 8-12 minutes, or until the tart shells are light golden brown and cooked through.
7. Cool: Let the tart shells cool in the pans for 5-10 minutes before carefully removing them to a wire rack to cool completely. If they stick slightly, a gentle twist or a thin offset spatula run around the edge can help.

Part 3: Making the Vanilla Cream Filling (Pastry Cream)

1. Infuse Milk (if using vanilla bean): In a medium saucepan, combine the whole milk and the scraped vanilla bean pod and seeds. Heat over medium heat until it just begins to simmer (small bubbles around the edges). Remove from heat, cover, and let steep for 15-20 minutes to infuse the vanilla flavor. If using vanilla extract, skip this steeping step and add the extract at the end.
2. Whisk Yolks, Sugar, and Cornstarch: In a separate heatproof medium bowl, whisk together the large egg yolks and granulated sugar until pale and slightly thickened. Then, whisk in the cornstarch until smooth and no lumps remain.
3. Temper the Eggs: If you steeped the milk with a vanilla bean, remove the pod. Gradually pour about half of the hot (or warm, if not steeped) milk into the egg yolk mixture, whisking constantly. This tempering process prevents the eggs from scrambling.
4. Cook the Custard: Pour the tempered egg mixture back into the saucepan with the remaining milk. Cook over medium-low heat, whisking constantly and vigorously, especially around the edges and bottom, to prevent scorching and lumps. Continue whisking until the pastry cream thickens considerably and comes to a gentle boil. Boil for 1-2 minutes, still whisking, to fully cook out the cornstarch. It should be thick enough to coat the back of a spoon heavily.
5. Finish and Chill: Remove the saucepan from the heat. Whisk in the softened tablespoon of unsalted butter until smooth. If you are using vanilla extract instead of a bean, stir it in now.
6. Strain (Optional but Recommended): For an ultra-smooth pastry cream, strain it through a fine-mesh sieve into a clean bowl. This will remove any potential small lumps or bits of cooked egg.
7. Chill the Cream: Press a piece of plastic wrap directly onto the surface of the pastry cream to prevent a skin from forming. Refrigerate for at least 2-3 hours, or until completely chilled and set. It will thicken further as it cools.

Part 4: Assembling the Mini Fruit Tarts

1. Prepare the Cream: Once the pastry cream is thoroughly chilled, give it a good whisk to loosen it up and make it smooth and pipeable/spreadable.
2. Fill the Tart Shells: Carefully spoon or pipe the chilled vanilla cream filling into each cooled tart shell, filling them almost to the top.
3. Arrange the Fruit: Artfully arrange your chosen fresh fruits on top of the cream filling. Get creative with patterns and color combinations! You can slice larger fruits like strawberries or kiwis, and leave smaller berries whole.
4. Glaze (Optional): If using, gently warm the apricot jam or redcurrant jelly with the teaspoon of water in a small saucepan or microwave until melted and smooth. Strain if necessary to remove any lumps. Lightly brush the warm glaze over the fruit using a pastry brush. This adds a beautiful shine and helps keep the fruit fresh.
5. Chill Before Serving: Refrigerate the assembled mini fruit tarts for at least 30 minutes before serving. This allows the flavors to meld and the tarts to firm up slightly.