01 - Set oven temperature to 375°F (190°C) to prepare for baking.
02 - Roll out pastry and line a 9-inch (23 cm) tart tin. Trim edges and prick base with a fork. Chill dough for 10 minutes.
03 - Line pastry with baking paper and fill with baking beans. Bake for 15 minutes, then remove paper and beans and continue baking for 5 minutes until golden.
04 - In a skillet over medium heat, cook bacon lardons until crisp. Drain on paper towels. In the same pan, sauté onion until translucent, about 3 minutes.
05 - Whisk together eggs, cream, milk, salt, pepper, and nutmeg in a large bowl until smooth.
06 - Distribute cooked bacon, sautéed onion, and half of the grated cheese evenly over the pastry base. Pour custard mixture on top, then sprinkle remaining cheese and optional chives.
07 - Bake for 25 to 30 minutes until filling is set and golden brown.
08 - Allow quiche to cool for 10 minutes before slicing and serving.