Using your food processor, combine the flour, salt and very cold butter and process for about 5 seconds. Sprinkle the cold water over the flour mixture and pulse until the pastry just begins to come together, about 10 seconds; you should still be able to see small pieces of butter in it. Add more water if needed.

Transfer the pastry dough to a lightly floured work surface, gather it together to combine everything and roll out to a 12-inch circle. Transfer the dough to a prepared, parchment lined baking sheet and refrigerate for about 20 minutes if you have time. (You can also roll out the dough and use it right away if needed).

Preheat your oven to 400 degrees. Remove your dough from the refrigerator and brush on the sour cream, in the center of the dough, leaving at least a 2-­inch border all around. Sprinkle on the garlic, lemon zest and season with salt and pepper.

Layer on the spinach evenly over the top, as well as the mushrooms and artichoke hearts. Sprinkle on the shredded mozzarella cheese. Gently fold over the pastry border, overlapping the edges as much as possible and gently press the folds together.