Preheat oven to 200C. Place whole potatoes on a tray, drizzle with olive oil, and roast for 1 hour or until tender.
Reduce oven temperature to 180C. Grease a springform pan.
Transfer potatoes to the pan and use the base of a cup to squash firmly into an even crust over the base and up the sides. Drizzle with olive oil.
In a bowl, whisk eggs, milk, and cottage cheese until combined.
Fold through spinach, feta, dill, mint, chives, lemon zest, and salt.
Pour mixture into the potato crust and smooth the top.
Sprinkle with mozzarella.
Bake for 45 minutes, until set and golden.
Rest for 10 minutes before slicing.
