Fry onion and garlic in olive oil for a few minutes
Add spinach and herbs, fry until water has evaporated, then leave to cool on a plate
Separate 1 egg, saving the yolk for brushing pastry
Whisk 4 whole eggs and 1 egg white with milk and set aside
Heat oven to 180°C and line a 20x30cm dish with parchment paper
Add pastry to dish and brush all around with egg yolk, including edges
Fork holes in the pastry base
Spread spinach mixture over pastry
Add cheese slices on top of spinach
Pour egg and milk mixture over cheese
Top with asparagus, salt, pepper, and optional grated cheese
Bake for 50-60 minutes on medium to low shelf
If getting too dark after 30 minutes, reduce oven to 170°C
Leave to cool for 15 minutes before serving
Serve hot or cold, store in fridge for up to 3 days
