01 - Combine flour and salt in a large bowl. Add cold butter and rub into flour until mixture resembles breadcrumbs. Mix in egg and enough water to bring dough together. Shape into a disk, wrap, and refrigerate for 30 minutes.
02 - Preheat oven to 375°F. Lightly grease a 9-inch tart pan with butter or cooking spray.
03 - Roll out chilled dough on a floured surface to fit the pan. Carefully transfer dough to tart pan, pressing into edges. Trim any excess dough from the rim.
04 - Whisk together ricotta, chopped spinach, Parmesan, 3 eggs, heavy cream, nutmeg, salt, and pepper in a large bowl until thoroughly combined and smooth.
05 - Spread half the ricotta mixture evenly into the pastry shell. Create 4 evenly spaced indentations using the back of a spoon. Carefully crack one egg into each well.
06 - Gently spoon remaining ricotta mixture around and over the cracked eggs, taking care not to break the yolks. Ensure eggs are mostly covered but yolks remain intact.
07 - Bake for 40-45 minutes until filling is completely set and surface is lightly golden brown. The center should not jiggle when gently shaken.
08 - Let tart cool in pan for at least 15 minutes to allow filling to set. Slice into wedges and serve warm or at room temperature.