Place the 4 large eggs in a large bowl, and whisk well to beat them. Then whisk in the 2 cups granulated sugar, reserving ½ cup of sugar, 1 cup olive oil, ⅓ cup orange juice, 2 teaspoons pure vanilla extract, 3 ½ cups whole grain flour, 3 teaspoons baking powder, ½ teaspoon fine sea salt and reserving ½ cup of the sugar, in the order in which they are written. Let it sit while you peel and cut up the apples. Mix the 2 large apples with 3 teaspoons ground cinnamon and remaining ½ cup of sugar.
Add half of the batter to the tube pan, sprinkle it with half of the cinnamon apples, then top with the remaining batter and spread the remaining cinnamon apples across the top. Rest the batter for another 10 minutes to hydrate the flour.
Place in the oven and bake for 1 ¼– 1 ½ hours, until a tester inserted comes out clean. Remove from the oven and cool in the pan for 30 minutes, then turn gently out onto a rack to cool completely.
Notes
What type of apple? My answer: Any type! In my opinion, any type of apple you have will work fine in this recipe, or do a combination of different varieties of apples.
Prepare batter in order of ingredients. The reason this recipe works so beautifully as a one-bowl method is that the batter is prepped following the order in the ingredient list. For example, add the eggs to the bowl first, whisk them, then proceed with adding the rest of the ingredients.
Another pan. If you don't have a tube pan, use a 10-inch springform pan or similar.
Place the cake on a baking sheet. When using a tube pan, batter can sometimes leak out the bottom. To prevent any spillage and yucky burnt bits on the bottom of the oven, place the pan on a baking sheet to catch any extra batter.
Try brown sugar. For a lovely hint of caramel complement to the apples, use brown sugar instead of the granulated sugar to mix with the apples (you'll swap ½ cup of the granulated sugar for brown sugar when you mix up the apple pieces).
Use butter. While I dearly appreciate that this cake is dairy-free, if you're yearning for a super-rich, buttery undertone, use 1 cup of unsalted butter instead of the olive oil. If you go this route, cream the butter and sugar first before adding the rest of the ingredients.
A little almond flour. Swap ¾ cup of the oat flour for almond flour for extra moisture and protein.
Add nuts. Stir in some chopped pecans or walnuts to the batter for crunch.