Preheat your oven to 180°C (350°F) and grease the muffin tins with butter.
Using a bowl, strain the flour, baking powder, and a pinch of salt, then set aside.
In a bigger mixing bowl, combine eggs and sugar.
Mix until you get a pale texture, then add the melted butter, vanilla extract, and fresh orange juice.
Continue mixing to combine everything evenly.
Add the milk, the sifted dry ingredients from earlier, and the grated orange zest.
Mix --- just enough to combine.
Spoon the orange tart batter into the prepared muffin tins. (Notice that it almost fills the rim because it will not rise as high as a muffin or cupcake.) Sprinkle some sugar on top of each tin.
Place the muffin tray in the oven for twenty to twenty-five minutes or until they turn golden on top and sides.
Take the tray out of the oven and let cool for at least ten minutes.
Remove your Portuguese orange tarts from the tin and serve.
Sprinkle with powdered sugar, if preferred, and enjoy!