Preheat oven to 375°F (190°C). Prepare the crust by combining dry ingredients, cutting in butter, adding water, then baking for 15-18 minutes. Cool completely.
Heat milk until steaming. Whisk sugar, cornstarch, and egg yolks. Temper with hot milk, cook until thickened, then stir in vanilla and butter. Chill until cool.
Spread custard into cooled tart shell, arrange berries on top, and brush with warmed apricot jam if desired. Refrigerate for at least 1 hour before serving.
Notes
For a glossy finish, brush the berries with warm jam before serving.