Preheat the oven to 180˚ C (350˚F). For the muffins, grate the orange and squeeze out 3 tbsp of juice. Pour the juice over the raisins in a bowl, stir in the grater and let it soak while you make the rest of the batter. The muffins are easiest to make in silicone molds which you briefly grease.
Mix the flour with 1 tsp baking powder, baking salt and cinnamon.
Separate one of the eggs. Put the egg whites in a small bowl and the yolks in a large bowl. Crack the remaining egg into the yolks and then add the sugar. Beat this for 1-2 minutes or until thick and frothy. Slowly pour in the oil and continue to mix on low speed until well blended. Add the flour mixture in two parts and gently stir in with a large spoon or rubber spatula. The mix will be quite stiff. Add the extra bit of baking powder to the egg whites and beat to soft peaks.
Stir the carrot and raisins (and any remaining liquid) into the flour mixture. Fold in the egg whites, then divide the batter among the muffin tins. Pat the countertop briefly to even out the batter. Bake the muffins for about 20-30 minutes or until a wooden skewer comes out clean.
To make the frosting, stir the cream cheese with the orange juice. Add the powdered sugar and orange zest. Do not beat this for too long. Stir in the lemon juice. When the muffins are completely cooled spread the frosting over the muffins. Then - optionally - sprinkle with some more orange sprinkles.