Add the flour, and salt in the bowl of a food processor and pulse a couple of times to combine.
Add the Colavita olive oil and pulse until it resembles a coarse meal.
Add in the ice water, one tbsp at a time, pulsing, until large clumps begin to form.
Pour the mixture out onto a clean surface and form into a ball then flatten into a disc. Wrap the dough in plastic and refrigerate for at least one hour (can be prepared the day before).
Heat the olive oil in a medium skillet over medium-high heat. Add the leeks and cook, stirring often, until softened, about 6 minutes. Season with salt and pepper, then add Dijon mustard, cream and half the fresh rosemary. Cook until the cream has reduced by half and the mixture is thick, about 5 minutes. Taste for seasoning and adjust as needed. Let cool completely.
When ready to assemble the crostata, preheat the oven to 375 °F and line a sheet pan with parchment paper.
Roll the dough out on a floured surface until it is about ¼ inch thick and 14-16 inches around. Gently roll the dough up on to the rolling pin and transfer it to the center of the parchment-lined pan.
Spread the cooled leek mixture evenly around the dough, leaving a 2 inch border on the outside.
Arrange the pears in a circular pattern on top of the leeks. Feel free to overlap them for a pinwheel effect.
Sprinkle the blue cheese and the walnuts on top of the pears.
Garnish with the remaining rosemary, a pinch of salt and a drizzle of Colavita EVOO.
Carefully gather the outer border of dough and fold it up and over the filling to form a 1 to 2 inch crust.
Brush the outer crust with egg wash (this will produce a prettier, more golden-brown crust).
Bake for 30-40 minutes or until the crust is golden brown.
Let cool for 30 minutes before slicing. Serve warm or at room temperature.