For the crust, set a rack in the middle level of the oven and preheat the oven to 350 degrees.
On a floured surface, pound the dough gently to soften it and roll it into a rectangle about 7 inches wide and 12 to 15 inches long. Trim edges and arrange on baking pan. Cut two 1-inch strips from the length of the dough, leaving a 5-inch wide rectangle. Pierce the large rectangle well with a fork and wet the long ends with water, using a pastry brush. Apply the strips of dough to the moistened edges and press down well with fingertips to make the strips adhere to the base. Indent the sides of the strips with the back of a paring knife and pierce the narrow strips at 1/2-inch intervals with the point of a paring knife. Chill the tart crust for an hour.
For the pastry cream, bring milk to a boil with half the sugar in a small saucepan. Whisk yolks in a bowl and whisk in remaining sugar and flour. Whisk the milk into the yolk mixture, then return mixture to the pan over the heat and whisk constantly until the custard boils and thickens. Remove from heat and whisk in vanilla and butter. Scrape the filling into a non-reactive bowl and press plastic wrap against the surface. Refrigerate until cold.
To bake the tart crust, place it in the oven and bake for about 30 minutes, until well risen and deep golden. Cool in the pan on a rack.
To finish, spread the pastry cream in the cooled crust and scatter the berries over the pastry cream, covering it entirely. Dust with confectioners' sugar immediately before serving.