For the pastry:

In a large bowl, combine the flour, sugar, and salt. Cut the cold butter into cubes about 1/2 inch in size. Add to the bowl  and work it into the dry ingredients with your fingers until the butter resembles the size of small walnut pieces.

Make a well in the middle of the bowl and gradually add the chilled water until the dough begins to come together into a rough ball. Continue to add small amounts of water until the dough ball becomes moist but not sticky and no dry flour remains on the dough ball. Knead the dough several times until it forms a smooth ball (do not over-knead). Form the dough into two small discs, cover with plastic wrap and chill in the fridge for 30 minutes. If you only need 1 disc of dough, the other disc can be frozen until needed.

For the filling:

Peel the peaches; cut the plums, apricots, peaches, and strawberries in 1/2 inch wedges. Add them to a bowl along with the fresh blueberries and sliced Kiwi fruit (if using). Add 1 Tbsp. flour, 1 Tbsp. sugar, orange zest, and lemon juice;  toss until coated and set aside.

For the crumb topping:

Add the flour, sugar, and dash salt in a bowl. Cut the chilled butter into rough cubes of 1/2 inch. Using your hands, work the butter into the dry ingredients until the dough starts to come together; set aside.

To assemble the crostata:

Pre-heat over to 425 F. On a lightly-floured surface, roll out the chilled dough into an 11-inch circle.  Transfer dough to a parchment-lined baking sheet. Brush the dough surface with several tablespoons of orange marmalade to prevent bottom of dough becoming soggy. Add 2-3 cups of the fruit on top of the dough, leaving a margin of 1 1/2 inches around the edges. Sprinkle the crumb topping on top of the dough. Gently fold the the edges of the dough over the fruit, pleating it to make an edge. Brush the edges of the folded dough with egg wash to help the dough  turn golden during baking. Bake at  425 F or 25-40 minutes or until the dough turns crisp and golden and the fruit softens. If the dough starts to burn, place some aluminum foil over the  top. Remove from oven and let cool for 5 minutes. Serve warm or at room temperature.