Tart Bacon, Telur dan Jamur (Puff Pastry)

Bahan-bahan (4 porsi)

• 5 eggs
• 1 tbsp Dijon mustard
• 2 tbsp thick sour cream or creme fraiche ((or sub with mayonnaise))
• 2/3 cup grated gruyere cheese (, separated (2 x 1/3 cup) (or any other melting cheese))
• Salt and pepper
• 1 sheet store bought frozen puff pastry (, thawed (25 cm x 25cm / 10" x 10"))
• 1 tbsp butter ((salted or unsalted))
• 5 oz / 150g mushrooms (, sliced (approximately 2 cups of sliced mushrooms))
• 6 - 8 oz / 200 - 250 g bacon (, roughly chopped)