Preheat oven to 400°F.
Place sliced strawberries and rhubarb in a saucepan.
In a small bowl, mix sugar and cornstarch.
Sprinkle the sugar mixture over the fruit and toss until evenly coated.
Heat the fruit on medium heat and brig to a simmer. Cook the mixture for 7-10 minutes until juices are released and thickened.
Turn off the heat and stir the vanilla into the fruit mixture.
Allow the fruit to cool completely.
Roll out chilled dough on a lightly floured surface to a 15-inch diameter.
Line a baking sheet with parchment paper or a Silpat.
Fold the dough into quarters, transfer to the baking sheet, and unfold.
Spread the fruit mixture in the center of the dough, leaving a 2½-inch border.
Fold the edges of the dough over the fruit, pleating as you go, leaving the center open.
Brush the pastry with an egg wash (egg yolk mixed with water) and sprinkle with sugar.
Bake for 35-40 minutes until the pastry is golden brown and the fruit is bubbling.
Once cool, move the tart to a large plate, gently pulling the parchment from underneath.
Arrange fresh strawberries in the center of the tart.
Serve with vanilla ice cream or whipped cream.