Begin by preheating your oven to 350°F (175°C).

To make the crust, in a mixing bowl, combine the flour, powdered sugar, and a pinch of salt. Add the softened butter and mix until crumbly.

Add the egg yolk and cold water to the mixture and knead gently until it forms a dough.

Roll the dough out on a floured surface to fit your 9-inch tart pan. Transfer it to the pan, pressing it into the edges. Trim excess dough.

Place baking paper over the crust and fill it with pie weights or dried beans. Bake in the preheated oven for 20 minutes. Remove the weights and paper, and bake for an additional 10 minutes or until golden brown. Set aside to cool.

While the crust cools, prepare the custard filling. In a saucepan over medium heat, combine the milk and half of the sugar, stirring until warm but not boiling.

In a separate bowl, whisk together the egg yolks, cornstarch, the remaining sugar, and a pinch of salt until smooth.

Slowly pour the warm milk mixture into the egg yolk mixture, while whisking continuously to avoid curdling.

Return the mixture to the saucepan and cook over medium heat, stirring constantly until it thickens and bubbles (about 5-7 minutes). Remove from heat and stir in the vanilla extract.

Pour the custard into the cooled tart crust and smooth the top. Allow it to cool to room temperature, then refrigerate for at least 2 hours to set.

Before serving, arrange the sliced strawberries, blueberries, and raspberries on top of the set custard. Drizzle with honey if desired and garnish with fresh mint leaves, if using.

Slice the tart into wedges and serve chilled.