This is a refreshing dessert. Simple and elegant, it is the perfect option to use when unexpected guests arrive, since it takes less than 10 minutes to prepare if you have frozen puff pastry at home. It looks beautiful on the plate, and provides a vibrant explosion of color and flavor to your table. —Andreina Morales
Preheat the oven to 350ºF and cover a baking tray with parchment paper.
Sprinkle your work surface with flour, and with the help of a rolling pin extend the puff pastry sheet until you have a thin rectangle of about 12x8inches. Place the dough on the parchment paper -covered tray.
With the help of a brush, paint the dough with a thin layer of jam.
Sprinkle the blackberries and blueberries over the dough. Then sprinkle with the sugar, and place the butter cubes over the fruit, trying to evenly distribute them over the entire surface.
Bake for approximately one hour, or until the dough turns golden brown.
Meanwhile, in a small saucepan, bring the remaining jam to a boil. Pass through a sieve and reserve.
When the tart is ready and still hot from the oven, brush again with a thin film of the hot jam to give it some shine. Then use an off-set spatula to separate the dough from the parchment paper to ensure it does'nt stick as it cools down.
With a pizza cutter, cut out any rough edges and cut out individual portions to serve.