1. Preheat oven to 350F (180C).
2. Peel apples. Quarter each apple and remove the core with a diagonal cut. Cut each quarter into three lengthwise then thinly slice.
3. In a large bowl using an electric mixer (I used KitchenAid stand mixer), beat together eggs and sugar on high speed for about 5 minutes.
4. Add Greek yogurt and beat for another minute.
5. Add flour and baking powder, mix on low for another minute or two, scraping down the sides, if necessary.
6. Grease bottom and sides of your baking dish with ghee (I had an 8”x8” (~20cmx20cm) glass dish)).
7. Add batter to the greased baking dish, top with lemon zest and thin apple slices. You can use a spatula to evenly distribute apples.
8. Cover with foil and bake in the center of the oven for 35 minutes. Remove foil and bake for another 5-7 minutes (depending on your oven, until the center is set). Remove from the oven, let cool, cut into portions and serve.