Preheat oven to 350°F (175°C). Lightly grease an 8-inch round pan or line the bottom with parchment. In a large bowl, beat eggs and sugar together until very light, thick, and pale (about 4–6 minutes with a mixer — this step is key). Beat in vanilla if using. In a separate bowl, whisk flour, baking powder, and salt. Gently fold dry ingredients into the egg mixture using a spatula. Do not overmix — keep as much air as possible. Pour batter into prepared pan and smooth the top. Bake 25–30 minutes, until: Top is lightly golden Cake springs back when touched A toothpick comes out clean Cool 10 minutes, then remove from pan and cool completely.