Smoked Haddock and Spinach Tart

Pastry

• 200 g plain flour, plus extra for dusting
• 100 g unsalted butter, cold, diced
• 1 pinch fine sea salt
• 50 g milk, cold

Filling

• 50 g Cheddar cheese, cut in pieces (2 cm)
• 300 - 350 g smoked haddock
• 1300 g whole milk
• 150 g onions, finely sliced (2 mm)
• 10 g olive oil
• 10 g unsalted butter, diced
• 300 g fresh spinach leaves
• 50 g water

Cooking

• 3 medium eggs, 1 separated
• 100 g double cream
• 1 pinch fine sea salt
• 1 pinch ground black pepper