Preheat the oven to 375°. Mix together the soft cheeses with part of the egg, and set aside both the cheese mixture and the remaining egg. Prepare your vegetables and/or meat; grate the melting cheese.

Roll dough out to a large circle a scant ¹/₄" thick. Leave the edges rough, and transfer to a baking sheet. Leaving a 1" border all round, spread the soft cheese all around the bottom of the tart. Top with your feature layer, and then distribute the melting cheese on top. Fold the edges over to overlap with the edge of the filling, folding every three or four inches.

Brush the edges with the reserved beaten egg. Bake for 30 minutes or until golden brown on the edges and the cheese is nicely melted. Serve right away.