1 sheet frozen puff pastry
Prep the tart shell: Allow the puff pastry to defrost in the refrigerator, for about 2 hours or so, until it can be unfolded easily without ripping. Unroll onto a parchment-lined baking sheet. Score a 1/4-inch border with a paring knife along the edge of the pastry. Make an egg wash by mixing one yolk with 1/2 tsp water. Brush this egg wash along the border, only using as much as you need. Place in the freezer until you are ready to use.
Scatter the remaining grated gruyere, and then the bacon-scallion mixture, evenly over the tart. Bake until the cheese is bubbling and the crust is golden brown, rotating the baking pan half-way through, for a total baking time of about 25 minutes. Be sure to lift up the edge of the tart and take a peek at the bottom side, to make sure the crust is cooked through. Remove from the oven, and transfer the tart to a cutting board. Slice six by four, to get bit-sized pieces. Sprinkle with the parsley, tarragon, chervil and chives, then season with a sprinkling of salt and pepper. Serve right on the cutting board, for a rustic presentation.