In a saucepan, melt butter with milk, set aside to cool slightly.

In the bowl of a mixer, place eggs (whole, without separating whites and yolks), sugar, and vanilla extract. Beat (with a whisk attachment for egg whites) until the egg mixture is very fluffy, foamy, and doubles in volume (about 7 minutes on high mixer speed). Alternately add sifted dry ingredients and the warm butter mixture to the egg mixture in two batches. Mix briefly or fold with a spatula.

Grease a 23 x 33 cm baking pan with butter and line it with parchment paper. Pour the prepared batter into the pan. Bake at 160ºC for about 40 minutes or until a toothpick comes out clean.

While the cake is baking, prepare the milk mixture. Combine all ingredients in a bowl and mix well until combined.

Remove the baked cake from the oven and let it cool for 10 minutes. Afterward, poke the cake with a skewer. Slowly, spoon by spoon, soak the cake with the prepared milk mixture. The cake will become increasingly moist, absorbing the milk like a sponge.

After soaking, let the cake cool to room temperature, then chill it in the refrigerator for 3 hours.