01 - Mix flour and salt in a large bowl. Add cold butter and rub into flour until mixture resembles coarse breadcrumbs. Add egg and 2-3 tablespoons cold water, mixing until dough just comes together. Shape into a disk, wrap in plastic, 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 a 11-inch circle. Carefully transfer dough to tart pan, pressing into corners. Trim excess dough from edges.
04 - In a large bowl, combine ricotta, chopped spinach, Parmesan, 3 eggs, cream, nutmeg, salt, and pepper. Whisk until completely smooth and well incorporated.
05 - Spread half the ricotta mixture evenly into the tart shell, smoothing with a spatula.
06 - Using the back of a spoon, create 4 evenly spaced shallow wells in the filling. Carefully crack a medium egg into each well, keeping yolks intact.
07 - Gently spoon remaining ricotta mixture around and over the eggs, leaving yolks exposed. Take care not to break yolks during this process.
08 - Bake for 40-45 minutes until filling is completely set and top is lightly golden brown. The center should not jiggle when gently shaken.
09 - Let tart cool in pan for at least 15 minutes before removing. Slice and serve warm or at room temperature.