01 -  Preheat the oven to 180°C (350°F). 
 02 -  Roll out the pastry and line a 24 cm (9-inch) tart tin. Trim excess pastry and prick the base with a fork. Place in the refrigerator for 10 minutes. 
 03 -  Line the pastry with parchment paper and fill with baking beans. Blind bake for 12 minutes. Remove the paper and beans, then bake for another 5 minutes until lightly golden. 
 04 -  Heat olive oil in a skillet over medium heat. Add the diced red onion and sauté for 2–3 minutes until soft. Set aside to cool. 
 05 -  In a large bowl, whisk together the eggs, crème fraîche, and milk. Stir in salt, pepper, and nutmeg. 
 06 -  Scatter the sautéed onions, halved cherry tomatoes, and torn basil leaves evenly over the baked pastry base. Sprinkle with grated cheese. 
 07 -  Pour the egg mixture over the filling, ensuring everything is evenly covered. 
 08 -  Bake in the preheated oven for 25–30 minutes until the filling is set and the top is golden. 
 09 -  Let cool for 10 minutes before slicing. Serve warm or at room temperature.