Leek and gruyere tart - 9Kitchen

Ingredients

• 6-8 leeks (1.5kg), white part only
• 50g unsalted butter
• 2 tablespoons olive oil
• salt and pepper, to taste
• 300ml pouring cream
• 4 eggs
• 1 cup grated gruyere cheese
• extra sour cream and salad leaves, to serve
• 1½ cups plain flour
• 125g cold salted butter, chopped
• ¼ cup sour cream