On a lightly-floured surface, roll the dough into an 11x14-inch rectangle. Transfer the rectangle to a parchment-lined baking sheet.
Spread the mustard over the lower half of dough, keeping a 1-inch border all around. Sprinkle the dried herb evenly over the mustard, then layer on the salami. Top the salami with the cheese.
Paint a one-inch strip of egg wash all around the pastry. Then fold the upper half of the pastry over the filled lower half, and press the edges to seal. Pop the works in the fridge for at least 15 minutes.
When you are ready to bake, preheat the oven to 450°F. Paint pastry top with beaten egg, and cut three venting slits into the top.
Bake until the pastry puffs and browns dramatically -- 20-25 minutes. Cool on the baking sheet for 10-15 minutes before the cutting the pastry into 15 2-inch by 1-inch rectangles. Serve warm or at room temperature.