Prepare the Milk Mixture: In a medium saucepan, combine the whole milk, milk powder, wheat starch, granulated sugar, water, and salt. Whisk gently until all ingredients are well combined and the sugar begins to dissolve.

Heat Gently: Place the saucepan over medium-low heat, stirring constantly. Heat the mixture until it is warm to the touch and the sugar is fully dissolved. Do not bring it to a boil. Remove from heat immediately and set aside to cool completely to room temperature. This step is crucial to prevent the eggs from scrambling later.

Whisk and Strain Eggs: While the milk mixture cools, lightly whisk the 3 large eggs in a separate bowl. To ensure an incredibly smooth custard, strain the whisked eggs through a fine-mesh sieve into another clean bowl. This removes any chalazae or bits of egg white.

Combine Custard Ingredients: Once the milk mixture is completely cooled, gradually whisk the strained eggs into it. Add the vanilla extract, if using. For the smoothest possible custard, strain the entire combined custard mixture one more time through a fine-mesh sieve.

Preheat Oven & Prepare Shells: Preheat your oven to 200°C (390°F). Arrange the pre-made mini tart shells on a baking sheet.

Fill Tart Shells: Carefully pour the prepared custard mixture into each tart shell. Fill them approximately 80-90% full to allow for a slight rise during baking without overflowing.

Bake to Perfection: Bake for 15-20 minutes, or until the edges of the custard are set and slightly puffed, and the center still has a slight wobble. The custard should be a beautiful golden yellow. Avoid overbaking, as this can lead to a dry or rubbery texture.

Cool and Serve: Remove the baked egg tarts from the oven and let them cool on a wire rack for a few minutes before serving. They are delightful served warm or at room temperature.