Preheat the oven to 350°F.

In a mixing bowl, combine the flour and salt.

In another bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the egg yolk, cold water, and vanilla extract, mixing until well combined.

Gradually add the flour mixture to the butter mixture, stirring until a dough forms.

Press the dough into a 9-inch tart pan evenly across the bottom and up the sides.

Prick the bottom with a fork to prevent bubbling.

Bake for 15-20 minutes or until lightly golden. Remove from the oven and let cool completely.

In a separate bowl, toss the mixed berries with ¼ cup granulated sugar, cornstarch, and lemon juice. Let sit for about 10 minutes.

Spoon the berry mixture into the cooled tart shell.

In a mixing bowl, whip the heavy cream with powdered sugar and vanilla extract until soft peaks form.

Spread or pipe the whipped cream over the berries in the tart.

Chill the tart in the refrigerator for at least 30 minutes before serving.