This is a delicious yellow cake with a lovely crumb. The soaking it gets with the sugar syrup flavored with rum keeps it very moist. If you're a teetotaller and want to skip the rum, make a simple sugar syrup to soak it. Of course, then it's not "borracha" anymore, but I don't have enough Spanish to know what to call it - what's the word for "non-borracha"? (I also have a feeling that it would be very delicious without any soaking at all.)
Preheat oven to 350°F.
Butter and flour a 10" round cake pan.
In a medium bowl, combine dry ingredients: flour, baking powder, and salt. Stir or whisk gently until blended (or use a sifter).
In a large chilled bowl, beat whites until foamy and white. Gradually add 1/4 c. sugar, continuing to beat whites until soft, shiny peaks form.
In a separate medium bowl, with the same beaters, beat yolks with 1/2 c. sugar until thick and fluffy.
Fold yolks in to beaten whites until just blended.
Fold flour into the egg mixture gradually and carefully.
Drizzle in butter, vanilla.
Gently turn batter into prepared pan.
Bake 25–30 minutes at 350°F, or until lightly browned on top. While cake is baking, make one recipe of Rum Syrup
While cake is cooling, gradually spoon on Rum Syrup
until all is absorbed.
Cool to room temperature before serving.