Preheat oven to 400 degrees.

Set Pepperidge Farm puff pastry on a plate to thaw on the counter. Meanwhile, chop leeks, then place in a large bowl of cold water. Allow sediment and dirt from leeks to settle to the bottom of the bowl, drain and repeat a few times to be sure leeks are very clean.

Heat butter in large skillet over medium heat. Add leeks and 1/4 teaspoon of salt and saute until beginning to brown and reducing quite a bit, about 8 minutes. Add ham to the leeks and continue to saute about another 6-7 minutes. You want the mixture to be well-cooked and dry.

Beat 5 eggs, sour cream, the remaining 1/4 teaspoon of salt, dried mustard and dill in a bowl. Pour over cooking ham and leeks and cook until barely set... you want the eggs to begin to scramble, but still look a bit wet. Remove from heat to a clean bowl, fold in crumbled goat cheese and refrigerate for 20 minutes.

While waiting for egg mixture to cool, lay your puff pastry flat on a silicone baking mat. Sprinkle very lightly with flour and gently roll to almost the size of your baking mat (about a 12 x 10 inch rectangle). Lay the baking mat and pastry flat on a baking sheet.

Evenly arrange the cooled egg mixture on top of the pastry, down the middle, with about a 1-inch border on the top and bottom and a 3-inch border on each side. With a sharp knife, cut strips down each side of the puff pastry, about 1-inch thick.

Bring two strips at top and two strips at bottom and cross toward the center so as to seal the ends (see picture). Then starting at the top, criss cross strips over top of the other down the middle, as if "braiding".

Beat the remaining egg with one tablespoon of water and gently brush the top of the pastry until all sides are covered with egg wash. Sprinkle with poppy seeds, if desired.

At this point, you can cover your braid tightly with plastic wrap (on the baking sheet) and refrigerate overnight. Bake braid for about 30 minutes (if baking right away) or about 40 minutes (if baking from refrigerator) until puffed and nicely browned. Allow to cool for about 10 minutes, slice and serve.