Preheat oven to 425 degrees. Place rack in the center of the oven (this will help prevent the top of the crostata from burning).
To make the dough, in a medium size bowl, combine flour and salt, whisk together. Add the cold cubed butter, using a pastry blender, cut for 1 minute (you don’t want the butter to get too small). Gradually add the vinegar, then add one tablespoon of ice water at a time, using your hands to combine the mixture as you add (you might not need all of the water, you just want it to barely hold together). Place the dough onto a sheet of plastic wrap and cover tightly. Place in the refrigerator to chill for 30 minutes (while you prep the other ingredients).
Meanwhile in a large skillet over medium-low heat, add butter. When butter has melted add pears, cook for 5-8 minutes or until they become slightly soft. Remove from skillet and place into a large bowl. Toss with sugar, flour, cinnamon, lemon juice, lemon zest and walnuts- set aside.
Roll out pie dough into a 9″ circle (the edges don’t have to be smooth). Transfer to a rimmed baking sheet lined with parchment paper or a Silpat mat. Place the pear mixture into the center leaving about 2″ of edge around the mixture. To fold, bring up the edges and pinch 5-6 times to help “get rid” of excess dough. Pat firmly around the mixture.
Brush the pie dough edges with the egg, then sprinkle generously with turbinado sugar. Place in oven and bake for 30-45 minutes or until the crust is crisp and the pears are tender. Remove and allow to cool for 20 minutes before cutting and serving.