Squeeze the juice from half an orange and cut the peel into pieces. Place the orange peel into the mixing bowl and blend for 10 seconds / speed 10.
Place the orange peel, orange juice, eggs, and sugar into the mixing bowl. Mix for 3 minutes / 37°C / speed 5, then blend for another 3 minutes / speed 5.
Add the oil and mix for 15 seconds / speed 5.
Add the flour, baking powder, and salt, then mix for 8 seconds / speed 6. Transfer the batter into a piping bag and fill the muffin cases up to ¾ full. Let them rest in the fridge for 30 minutes. Meanwhile, preheat the oven to 250°C.
Sprinkle sugar on top of the muffins. Lower the oven temperature to 220°C and bake for about 15 minutes. Let them cool, then serve or store in an airtight container.