Preheat oven to 325F and grease and line a 2lb loaf tin.
Place the butter and sugar into a large bowl or the bowl of your stand mixer and beat until light and fluffy, about 2 minute on med-high speed.
Add in the eggs and vanilla extract, scraping down the sides as necessary, mix on med-high until well incorporated and smooth, around 1 minute.
Add the cake flour, baking powder and salt if using, mix on low-med until smooth.
Add in the mango purée/pulp and mix on low-medium until well incorporated, light and smooth.
Pour the cake batter into the lined loaf tin and level it off with a spatula/wooden spoon.
Place in the oven for 65-70 minutes until risen, golden and an inserted skewer into the centre comes out clean.
Leave to cool in the tin for at least 1 hour before transferring to a wire rack.
Once cool, make the glaze: Using a medium sized bowl, scrape the insides of the passion fruits into a sieve and use the back of a spoon to separate the juice from the seeds. Place seeds in a separate bowl, you can either discard them or use them as a garnish.
Add 1/2 cup sifted icing sugar into the passion fruit juice and mix until smooth and glossy.
Slowly spoon glaze all over the cooled cake and garnish with passion fruit seeds if desired.
Cake will keep in an airtight container, at room temp, for 3 days.