Preheat oven to 325 F and line an 8″ x 8″ cake pan with parchment paper.
Crack the eggs into a bowl, carefully separating the yolks and whites. Set the bowl with the egg whites aside.
To the bowl of egg yolks, add the sugar and beat until the mixture turns pale yellow, about one minute.
Add the vanilla extract and melted butter and beat until the ingredients are well incorporated, about 30 seconds to 1 minute.
Add flour and beat mixture until just combined.
Pour milk in ¼ cup at a time, beating the mixture each time after more milk is added. Set aside.
Take the egg whites and beat them with a mixer until stiff peaks form.
Gently fold the egg whites into the batter, one-third at a time, until just incorporated. Be careful not to knock the air out of the egg whites. The batter should be thin but lumpy.
Pour the batter into the prepared cake pan.
Bake until the top is golden brown and the cake does not jiggle when you gently shake the tin, around 40 to 50 minutes.
Once the cake cools, remove it from the pan and dust the top with powdered sugar.
Cut into slices and serve with whipped cream and fresh fruit, if desired.