Preheat your oven to 180c/160 fan and prepare a large sheet pan with parchment paper for easier cleanup and to ensure no sticking.
Crack the eggs into a large bowl and whisk with the milk, salt, and pepper until combined.
18 large eggs, 1/4 cup milk, 1/2 tsp salt, 1/2 tsp pepper
Place the broccoli, mushrooms, and wilted spinach evenly across the sheet pan.
250 grams chestnut mushrooms, thinly sliced, 1 medium head of broccoli, cut into very small florets, 120 grams spinach, blanched with as much moisture as possible squeezed out
Pour the egg and milk mixture over the broccoli and mushrooms.
Evenly sprinkle the grated Gruyère and chopped chives across the pan and evenly distribute a few extra grinds of black pepper.
75 grams shredded Gruyère, 2 tbsp fresh chives, chopped, Additional fresh black pepper
Bake in the oven for 20-25 minutes until the mixture sets.