Transfer the dough onto a floured surface.
Roll the chilled dough into a 12-inch (30 cm) circle on a lightly floured surface.
Transfer it to the prepared baking sheet.
Spread the ricotta mixture evenly over the dough, leaving a 2-inch (5 cm) border.
Arrange the tomato slices over the filling, slightly overlapping them.
Drizzle with the olive oil and season with a little black pepper.
Fold the edges of the dough over the filling, pleating as you go.
Brush the pastry with the beaten egg.
Bake for 40–45 minutes, or until the crust is deeply golden and crisp and the tomatoes are tender.
Let the galette cool for about 10 minutes before slicing. Finish with fresh basil and a sprinkle of flaky sea salt.