Preheat the oven to 200 °C (400 °F)
Slice the potatoes thinly (2 mm thick) using a mandolin. Set aside.
Add cream, nutmeg, garlic and thyme to a bowl, mix until combined. Set aside.
Unroll puff pastry and cover the bottom and sides of a tart tin (⌀ 24 cm)
Scoop sour cream onto the pastry and spread evenly.
Layer potatoes in little stacks. Place stacks upright onto the sour cream layer.
Pour the cream mixture on top.
Sprinkle with freshly ground black pepper and top with butter flakes.
Bake in the center of the oven for 40 minutes until golden and crispy.
Serve straight away.
