01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - Roll out the puff pastry onto the prepared baking sheet. Fold the edges inward to create a 1-inch border around the perimeter. Prick the base thoroughly with a fork to prevent excessive puffing.
03 - Bake the pastry for 10 minutes until lightly golden. Remove from the oven and gently press down any puffed areas to create an even base.
04 - In a large bowl, whisk together the eggs, milk, heavy cream, Dijon mustard, salt, black pepper, and smoked paprika until completely smooth and well combined.
05 - Distribute the cooked bacon, chopped spinach, halved cherry tomatoes, and sliced spring onions evenly across the pastry base. Sprinkle the shredded cheddar cheese over the vegetables.
06 - Pour the egg mixture gently over the fillings, ensuring even distribution. Return to the oven and bake for 25 minutes until the center is just set and the top is golden brown.
07 - Allow the tart to cool for 5 to 10 minutes before slicing. Garnish with freshly chopped chives and serve warm.