Preheat oven to 200°C (390°F) or 180°C (360°F) for fan-forced ovens. Line a standard 12 hole muffin tin with paper liners. Alternatively, use 10 mini loaf tins, grease and line them with baking / parchment paper.
For the dry ingredients - Whisk together flour, sugar, baking powder, and salt in a large mixing bowl to get rid of any lumps. Mix the chocolate chips into the flour mixture.
For the wet ingredients - In a separate bowl, whisk together the egg, butter, milk, passionfruit pulp and vanilla extract.
Make a well in the dry ingredients, then pour in the wet ingredients. Fold to combine just until there are no dry bits of flour showing. Don't over-mix the batter as this will make tough muffins. Divide the batter evenly in each muffin case, then bake for 16 to 20 minutes. The muffins are done when a skewer comes out clean when inserted in the middle (take care as it could be melted chocolate on the skewer and not raw batter) Allow muffins to sit in the tin for 5 minutes before moving them to a cooling rack.
For the frosting - Before frosting, make sure the muffins have cooled completely. Using a hand or stand mixer to beat together the cream cheese and butter. Beat on medium-high speed for around 2 minutes. Add in half of the icing sugar and continue to beat until combined, then beat in the remaining sugar until smooth. Add in the vanilla extract and passionfruit pulp, then beat until well combined.
The frosting should be thick enough to spread with a butter knife, but not too runny that it drips down the muffin. Increase the thickness of the frosting by adding more icing sugar gradually, using one tablespoon at a time, until it reaches the desired consistency. To make the frosting thinner, add a small amount of passionfruit pulp or milk. Optional - place a few teaspoons of passionfruit pulp over the frosting.