Pound cake

Take the butter out of the refrigerator so that it comes back to room temperature.

Mix well sugar and soft butter.
Break the eggs, reserving the whites and adding one by one the egg yolks in the preparation.
Mix well.
Preheat the oven to 180 °C (360 °F).

Then add the flour and the baking powder.
Beat the whites very firm, with a pinch of salt (unless the butter is already salted).
(Beating the whites is not mandatory but makes a lighter cake).
Add the egg whites to the preparation by gently lifting/mixing them (1/3 first, then the rest).
Pour the dough into a nonstick (or buttered) mold
Bake at 180 °C (360 °F) for 30 to 40 minutes.

Check the cooking: the blade of the knife planted in the heart of the cake should come out clean.

Serve cold (or just lukewarm).

"Quatre-quarts" (the cake's French name) is a reminder that each of the 4 main ingredients are in the same proportion. Like "Pound cake" means a pound of each. In Brittany this used to be a classic funeral meal cake.
Mediterranean version: replace butter with 140 g olive oil & 6 cl sweet wine. When beaten, the egg whites must become very firm. A bit of rum, orange blossom or bergamot can be added to the dough.
Like madeleine cakes you can add some zest of citrus in the dough and ice the top: mix 30 g of icing sugar with 10 g juice. Brush just at the end of baking an put back in a very hot oven 30 sec.