Instructions

1. Preheat oven to 400°F. Grease bottom and sides of a 9-inch round cake pan with olive oil. Line bottom of pan with a round piece of parchment paper; grease paper with more oil.
2. Grate 1 Tbsp zest and squeeze juice from 1 orange into 2 separate small bowls; set aside. Slice remaining 3 oranges crosswise in ⅛-inch-thick slices. Remove and discard any seeds from slices.
3. Add ⅓ cup sugar to reserved orange juice, whisking until slightly smooth. Spread mixture in an even layer in bottom of prepared cake pan. Arrange orange slices in bottom of pan.
4. Whisk cake flour, almond flour, baking powder, and salt in a medium-size bowl; set aside.
5. Beat eggs and 1 cup sugar with an electric mixer fitted with whisk attachment 3 to 4 minutes or until mixture is very pale and thick. With mixer running, slowly beat in ¾ cup oil until fully incorporated.
6. Beat in vanilla and reserved orange zest until smooth. Slowly beat in flour mixture until just combined.
7. Pour batter over orange slices in pan. Place cake in oven and immediately reduce oven temperature to 350°F. Bake 40 to 45 minutes or until golden brown and a wooden pick inserted in center of cake comes out clean.
8. Cool cake completely on a wire rack. To serve, invert cake onto a cake stand or serving plate, remove parchment paper, and slice.