Here’s a perfect snacking cake made with olive oil, plenty of citrus zest and whole-wheat flour. It's light (not dense, despite the whole-wheat flour) and with a texture somewhere between cake and banana bread. You can use whatever citrus you have on hand. Note that this recipe doesn't create a super-tall loaf, but instead makes perfect small slices for all-day snacking.
Preheat the oven to 350 degrees F. Lightly grease a 9-by-5-inch loaf pan with nonstick spray.
Rub the brown sugar, orange and lemon zests together in a medium bowl until well combined. Stir in the oil. Add the eggs one a time, whisking in each one well before adding the next. Whisk in the juice and vanilla.
Stir the whole-wheat flour, baking powder and salt together in a small bowl. Add the dry ingredients to the wet and mix with a rubber spatula just until incorporated. Pour the batter into the prepared pan and spread evenly. Sprinkle with the raw sugar if using.
Bake until a toothpick inserted into the center of the loaf comes out clean, 40 to 45 minutes. Cool the cake in the pan for 15 minutes, then remove from the pan and cool completely on a rack before slicing and serving.