Beat the eggs with the softened (not melted) butter and sugar. Add the flour and baking powder, then gradually add the water while continuing to beat.

Add the ground almonds and lemon zest.

Preheat the oven to 340°F (170°C). Grease a 10-inch (25 cm) round cake pan and pour in the batter. Bake for about 30 minutes. Check doneness by inserting a long skewer—if it comes out clean, the cake is done.

Let the cake cool, then remove from the pan. Dust the top with powdered sugar and, if you like, decorate with a Santiago cross stencil.