Peel the potatoes and cut into slices using a food processor. Grease the bottom of a gratin dish and sprinkle with oregano. Spread the potato slices evenly in this gratin dish. Cut the onion into thin rings and place on top of the potatoes form, mixing the mixture well. Sprinkle with salt and season with freshly ground black pepper. Beat the 2 eggs and mix them with a whisk, add the flour and milk and mix until smooth. Pour this mixture over the potatoes in the gratin dish and spread evenly so that all the potatoes are covered. Set the oven to 180 °C (convection oven) and place the gratin dish in the middle. After 50 minutes, check if the whole thing is nicely browned. Then sprinkle the feta and the parmesan on top. Put it back into the oven and continue cooking until the cheese has melted.
Already you have a real treat for the palate.