Preheat the oven to 375° F.
Beat the eggs with the sugar in a medium bowl.
Melt the butter. Continue to beat the egg mixture and slowly pour in the melted butter, making sure to mix thoroughly. Be sure that the butter has cooled slightly and is not bubbling when you add it to the egg and sugar mixture.
Stir in the lemon or orange zest, vanilla extract, and milk and mix until all the ingredients are combined.
Measure out the flour into a separate bowl and add the baking powder to it.
Add the flour mixture to the egg mixture, continuing to stir them until all ingredients are mixed well. The batter will be very thick.
Place paper liners into a cupcake pan. Use a large serving spoon to spoon batter into the liners, filling each one half full. Remember that the magdalenas will rise when baking! Place pans on the middle shelf of the preheated oven and bake them for 18-20 minutes until they have turned a golden brown color.
Remove the magdalenas from the oven and allow them to cool for 5 minutes before taking them out of the pan to cool some more. Use a teaspoon to sprinkle each magdalena with a dusting of the confectioners’ sugar.