1. Whisk together eggs, sugar and vanilla (you can use a mixer). Combine soda and flour, gradually add to the egg mixture, constantly stirring to avoid lumps.
2. Preheat oven to 350F (180C).
3. Peel and core apples, cut into quarters, then cut quarters into thin slices.
4. Layer the apples in a 9-inch round cake pan (previously buttered). Sprinkle with cinnamon and drizzle with lemon juice. If your apples are not sweet enough, you can sprinkle them with some sugar.
5. Pour the batter over apples, covering them all.
6. Bake for about 40 - 50 minutes, until a toothpick inserted in the center of the cake comes out clean.
7. Serve with milk or tea.