Preheat the oven to 350°F (175°C). Line the bottom of a 9x13-inch baking pan with parchment paper. Grease both the parchment and the sides of the pan with nonstick cooking spray to ensure the cake releases easily once baked.

In the bowl of a stand mixer fitted with the whisk attachment (or using a hand mixer and large bowl), combine 1 ¼ cups sugar, the eggs, citrus zest, and salt. Beat on medium-high speed until the mixture becomes pale, thick, and doubled in volume, about 5 minutes. This step is essential for achieving the light texture characteristic of this Spanish Sponge Cake.

With the mixer running on low speed, slowly pour in the olive oil and continue mixing until fully combined. Add the milk and vanilla extract, then mix briefly until incorporated. The batter should appear smooth and slightly glossy.

In a separate bowl, whisk together the flour and baking powder. Gradually add the dry mixture to the wet ingredients while mixing on low speed. Stop once all the flour is incorporated, taking care not to overmix. Use a rubber spatula to scrape the sides and bottom of the bowl to ensure all ingredients are evenly blended.

Transfer the batter into the prepared baking pan, smoothing the surface with a spatula. Evenly sprinkle the remaining 2 tablespoons of sugar over the top. This will create the traditional thin, caramelized crust during baking.

Place the pan on the center rack of the preheated oven and bake for approximately 30 minutes, or until the edges are golden brown, the top has formed a light crust, and a toothpick inserted into the center emerges clean.

Allow the cake to cool completely in the pan for about 1 hour before slicing. Once cooled, cut into squares or rectangles and serve. The cake’s delicate crumb and subtle citrus aroma make it ideal for breakfast, afternoon tea, or dessert.