Grease an ovenproof dish with oil. Fold the filo sheets into layers (see the video above the recipe) and arrange them snugly in the dish.They need to hold their shape, so it is important that the dish is not too large.
Tuck the courgette, potatoes and red onion in between the layers, and crumble the feta over the top.
Whisk together the eggs, crème fraîche, milk, garlic and thyme, season well with salt and freshly ground pepper and pour the mixture over the tart.
Drizzle a little olive oil over the top and bake in a preheated conventional oven (top and bottom heat) at 180°C for about 45 minutes.
Let the tart rest for 5-10 minutes before serving.