Preheat & Prepare – Preheat oven to 350°F (175°C) and grease a cake pan with butter or line it with parchment paper.
Whisk the Eggs – In a bowl, beat the egg whites until soft peaks form. In another bowl, whisk the whole eggs with sugar until light and fluffy.
Mix the Batter – Fold the beaten egg whites into the egg-sugar mixture. Add melted butter, lime zest, lime juice, and vanilla extract. Gently mix in the flour, baking powder, and salt.
Assemble & Bake – Pour the batter into the prepared pan and arrange the sliced apples on top. Bake for 30–35 minutes or until a toothpick inserted in the center comes out clean.
Cool & Serve – Let the cake cool before slicing. Dust with powdered sugar or drizzle with a lime glaze for extra flavor.