Preheat the oven to 400°F (200°C).
Roll out the puff pastry on a lightly floured surface.
Transfer the dough to a tart pan and trim excess edges.
Layer the sliced Brie cheese evenly over the pastry.
Spread the cranberry sauce over the Brie.
Cook the diced pancetta in a skillet until crispy and drain on paper towels.
Sprinkle the crispy pancetta and fresh thyme evenly over the tart.
Brush the edges of the puff pastry with beaten egg.
Bake in the preheated oven for 25-30 minutes or until golden brown.
Let the tart cool for a few minutes before slicing.
Serve warm and enjoy!