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.
Brush the folded edges of the crust with the beaten egg yolk and bake for about 30 to 40 minutes, or until the crust has become a lovely golden brown. Let cool for about 20 minutes before slicing. Garnish with the shaved Grana Padano cheese before serving. Enjoy.