Beetroot, feta and spinach quiche

Pastry

• 200 g buckwheat groats
• 1 pinch salt
• 100 g unsalted butter chilled and cut into pieces
• 45 g water
• plain flour for dusting

Filling

• 100 g brown onion cut into halves
• 1 garlic clove
• 250 g raw beetroot peeled and cut into quarters
• 5 eggs
• 400 g full cream milk
• 1 - 2 pinches salt
• 1 - 2 pinches ground black pepper
• 50 g fresh spinach leaves torn into pieces
• 100 g feta cheese cut into pieces (1 cm)