This is from Ratio a cookbook for the mathematician in every cook.
The ratio = 1 part butter : 1 part sugar : 1 part egg : 1 part flour
The following makes enough for one 9″ loaf pan. The books says it will mix better if doubled to the pound ratio. I have only made it as follows but I am sure it will mix better with more ingredients, unless you have a small mixer.
8 ounces butter, at room temperature, plus enough to butter the pan
8 ounces sugar
1 teaspoon salt
8 ounces eggs, at room temp. (about 4 large eggs, plus 1 large yolk), lightly whipped to combine
Juice and zest of 1 lemon
Juice and zest of 1 lime
1 tsp. vanilla extract
8 ounces flour (about 1 3/4 cup)
1 tsp. baking powder (optional, but I hedged my bet and added it)
For the citrus glaze:
1 Tbsp. lemon juice
1 Tbsp. lime juice
1/4 cup sugar
Preheat oven to 325F. Butter a 9-inch loaf pan.
In the bowl of a standing mixer, beat butter with paddle attachment for a minute. Add the sugar and salt and beat on med-high until the butter becomes very pale and volume has increased by about 1 third, 2-4 minutes.
Add the eggs slowly, so that they are gradually beaten into the batter, another minute or so. (If the batter appears to break, it should be ok when the flour is added.)
Add a tablespoon of each juice, all the zest and the vanilla.
Reduce the speed of the mixer to med-low. Add the flour. Mix only to incorporate the flour.
Pour batter into pan and bake 1 hour. Test, if blade or toothpick comes out clean remove and let rest 5 min. Turn out on rack to finish cooling.
Meanwhile, for the glaze combine the citrus juices and sugar in a small pan over med-high heat; stir until the sugar is dissolved. Taste to check the sweet-sour balance and adjust if necessary.
Brush cake with glaze on all sides.