In a dessert bowl pour in the warm orange juice or water and add in the sultanas. The warm liquid will help to plump them up while you mix the rest of the batter.
Preheat your oven to 220C/425F/Gas mark 7 and line or lightly grease a 12 hole muffin pan and place to one side.
In a large mixing bowl add in the flour, baking powder, salt and ground cinnamon and whisk it all together until well combined.
In a large jug or another mixing bowl combine the eggs, light brown sugar, sweetened condensed milk, olive oil and the vanilla extract and vigorously mix everything together.
Pour the wet ingredients into the dry ingredients.
Add in the grated apple and drain the sultanas and add these in to the batter.
Then with a gentle hand fold everything together, be careful not to overwork the batter at this point as you don't want tough muffins. Its ok if there are still a few lumps in the batter at the end.
Scoop the batter into the muffin pan, filling each hole about 2/3 of the way up. If you want an extra crunchy top then sprinkle a little sugar on top before baking.
Pop the muffins in your hot oven and bake for 5 minutes then reduce the heat in your oven to 190C/375F/Gas mark 5 and bake for a further 12 minutes. Check the muffins for doneness at this point. If a pick comes out of the centre clean then your muffins are baked through if not then give them a further minute or two.
Once baked through remove your muffins from the oven and allow them to rest in their pan for 5 minutes before transferring them to a wire rack to fully cool down.
Stored in an airtight container these muffins will last up to 5 days. They also freeze well for up to 3 months.