- Preheat oven to 350ºF (180ºC). Grease an 8x8" baking dish or line with parchment paper.
- Beat butter and sugar on medium speed of electric mixer until light and fluffy, about 2 minutes. Add egg yolks, one at a time, beating well after each. With mixer on low speed, add zest and juice from oranges. The mixture will appear curdled at first - that's ok. Increase mixer speed to medium and beat until it comes together, pausing to scrape down sides of bowl as needed.
- In a separate bowl, whisk flour and baking powder. With mixer speed on low, gradually beat into the butter mixture until just incorporated.
- In another bowl, whip egg whites until stiff peaks form. Fold 1/3 of the whites into the cake batter to lighten it up, then gently fold in the rest. (Use a light hand so you don't deflate the whites.) Scrape batter into prepared baking pan and bake for 35-45 minutes, until top feels springy when gently pressed and tester inserted in centre comes out clean or with just a few moist crumbs.
Recipe & Photo Credit: Jennifer Pallian, foodess.com *