Grease a quiche tin with olive oil and line it with baking paper if desired, to reduce clean-up and avoid sticking. Arrange the cooled, crushed potatoes in a single layer to form the base and sides of the tart. Press gently to create a rustic, even crust.

Prepare the filling by combining the sour cream, chopped spring onions, thyme, chives, salt, and cracked black pepper in a bowl. Spread this mixture evenly over the potato base, smoothing it out gently with a spatula.

Sprinkle the grated parmesan cheese generously over the top of the filling. This will help the top become golden and crisp during baking.

Preheat the oven to 200°C. Place the tart in the oven and bake for 30 minutes, or until the top is golden and the edges of the potatoes are crisp.

Remove from the oven and allow to cool slightly before serving. Garnish with additional chopped herbs if desired.