To make the pastry: combine the flour, sugar, salt, and lemon zest in a large mixing bowl. Add the butter and mix with a pastry blender or your hands until the mixture resembles coarse crumbs. Add the egg yolk and pour in the ice water; work it in to bind the dough until it holds together without being too wet or sticky. Squeeze a small amount together, if it is crumbly, add more ice water, 1 teaspoon at a time. Form the dough into a disk and wrap in plastic wrap; refrigerate for at least 30 minutes.
To make the filling: combine the peaches, blueberries, lemon juice, sugar, and flour in a large mixing bowl. Toss the mixture gently to coat the fruit.
Prepare your wooden burning brick oven according to manufacturer's directions or place a pizza stone in a conventional oven and preheat to 375 degrees F.
Sprinkle the counter and a rolling pin lightly with flour. Roll the dough out into a 14-inch circle, about 1/4-inch thick; it doesn't have to be perfect, free-form is the look you want for this rustic tart. Transfer the dough to a lightly floured pizza paddle. Spoon the fruit mixture into the center of the dough, leaving a 2-inch border all around; brush the border with the egg wash. Lift the edge of crust over the filling, leaving the fruit exposed in center. Gently fold and pinch the dough to seal any cracks. Brush the crust with the remaining egg wash and sprinkle with sugar. Bake the crostata directly on the brick oven floor towards the front or on the preheated pizza stone for 30 to 40 minutes or until the crust is golden brown and fruit is bubbly and tender. Slide a pizza paddle under the tart to remove it from the oven. Serve warm or at room temperature with vanilla ice cream.