Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

In a large bowl, combine the flour and salt. Add the chilled butter and mix until the mixture resembles coarse crumbs.

Gradually add ice water, one tablespoon at a time, mixing until the dough comes together. Form the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

On a floured surface, roll out the dough into a 12-inch circle. Transfer to the prepared baking sheet.

In a small bowl, mix the mayonnaise and Dijon mustard. Spread this mixture evenly over the dough, leaving a 2-inch border around the edges.

Layer the crumbled bacon, cherry tomatoes, spinach, and mozzarella cheese on top of the spread. Season with salt and pepper.

Fold the edges of the dough over the filling, pleating as necessary to create a rustic edge. Brush the exposed dough with the beaten egg.

Bake for 25-30 minutes, or until the crust is golden brown and the cheese is melted.

Allow to cool for 5 minutes before slicing and serving.