01 -
First, let's make those sweet orange toppings. Mix water with sugar in a pot and let it bubble on high heat. Once it's boiling, turn down to medium-low. Gently put orange slices into the sweet water, making sure they're mostly covered. Let them cook slowly for 15 minutes, moving them around now and then so they all get evenly soaked. They'll turn see-through and get a bit sticky. When done, stop the heat and wait till they cool enough to pick up with small tongs or your fingers. Save the orange-flavored syrup for later.
02 -
Put your oven rack in the middle and heat it to 350°F (175°C). Spray cooking oil all over a 9-inch springform pan, bottom and sides too. Put a round paper on the bottom so cake won't stick. Scrape the skin off both oranges for the batter, then cut away all white stuff under the skin (it tastes bitter). Chop peeled oranges into small chunks, taking out seeds and any leftover white parts. Throw orange bits and skin scrapings into a food processor and pulse till it looks like chunky applesauce.
03 -
Take your cooled orange slices and lay them out in a pretty pattern on the bottom of your greased pan. You can make circles from outside in or a spiral - whatever looks good to you. This will be the top of your cake when it's done. Set the pan aside while you make the batter. Keep that leftover sweet orange water for the end.
04 -
In your stand mixer with the whisk part, throw in eggs and sugar. Beat them on pretty high speed for about 5 minutes until they look pale and fluffy, like thick ribbons when you lift the whisk. While it's still mixing on lower speed, slowly pour in olive oil until it's all mixed in. In another bowl, stir together flour, salt, nutmeg if using, and baking powder. Switch to the paddle part or slow down the mixer and add dry stuff bit by bit until just mixed. Add your room-temp yogurt and mix it in. Last, add vanilla and your orange mush, stirring just enough to make everything smooth.
05 -
Slowly pour your cake mix into the pan over those arranged orange slices. Smooth the top with a spatula. Bake in your hot oven for 47-57 minutes. It's done when you stick a toothpick in the middle and it comes out clean or with tiny crumbs. The top should look golden and bounce back when you touch it. Start checking if it's done around 45 minutes since ovens can be different.
06 -
Let your cake sit in the pan for at least 30 minutes. This waiting part really matters - it helps the cake set up right. After waiting, run a knife around the edge to loosen it. Then open the springform clasp and take off the outer ring. Let the cake cool completely on the flat pan bottom before you flip it over.
07 -
When it's totally cool, put a serving plate on top of the cake and quickly flip everything over while holding both parts firmly. The cake should fall onto the plate with those pretty orange slices now on top. Carefully peel off the paper. For extra shine and sweetness, brush the saved orange syrup on top and sides. Cut slices and eat at room temp for best taste.