Put the Brie, brown sugar, yogurt or sour cream, half of the beaten egg and vanilla in a mixer and beat on low speed until all incredients are incorporated together.
Put the sugar, flour, and salt in a medium bowl and, using a table fork, mix until well blended. Add 1 cup of the blueberries and, using the table fork, crush the berries while stirring them into the sugar-flour mixture.
Add the Brie mixture and fold into the filling, then add the blackberries and toss to coat evenly. Spoon the filling into the lined tart dishes or muffin cups (they will be completely full). Scatter the streusel evenly over the filling.
Bake until the crusts and streusel are golden brown and the filling is bubbling, 25 to 27 minutes. Remove from the oven but leave it on.
Press 3 fresh blackberries into the center of each tart. Warm the jam and using a pastry brush, spread the warm jam over the fresh berries. Return to the oven for 2 additional minutes or until tester comes out clean. Remove from oven and let cool for 5 minutes.
Using a paring knife, run the blade between the crust and the pan to loosen the tarts from any sticky berry juices and let cool for 10 minutes..Using a thin, metal spatula carefully remove the tarts from the tart dishes or muffin cups and set them on a wire rack. Serve warm or at room temperature