Wash the spinach thoroughly and chop it finely.
Mix butter and sugar until light and fluffy.
Add eggs one at a time, mixing well after each addition.
Add chopped spinach and milk, and mix to combine.
Sift flour, baking powder, and salt together, then add to the mixture and blend evenly.
Pour the batter into a pound cake pan.
Bake in a preheated oven at 180°C for 40–45 minutes.
Cool completely on a wire rack.