01 - Preheat oven to 400°F. Roll out puff pastry and line a 9-inch tart pan, trimming excess. Prick base thoroughly with fork.
02 - Spread Dijon mustard evenly over pastry base.
03 - Whisk egg, crème fraîche, half the Parmesan, chopped basil, salt, and pepper. Pour over pastry base.
04 - Arrange mozzarella slices evenly, then layer tomato slices. Drizzle with olive oil and sprinkle remaining Parmesan.
05 - Bake 30–35 minutes until pastry is golden brown and filling is set.
06 - Cool slightly before garnishing with additional fresh basil. Serve warm or at room temperature.