For passionfruit curd, stir ingredients continuously in a small saucepan over low heat until mixture thickly coats the back of a spoon (5-6 minutes). Transfer to a bowl, cover and refrigerate to chill. Passionfruit curd will keep refrigerated for up to 2 weeks.
Preheat oven to 180C and line two 12-cup muffin tins (80ml per cup) with cupcake cases. Combine eggs and sugar in an electric mixer bowl, place over a saucepan of hot water and stir continuously until eggs are warm to touch (2-3 minutes). Place on the mixer and whisk on high speed until pale, frothy and tripled in volume (8-10 minutes). Sieve flour, baking powder and 1 tsp salt in and slowly whisk to combine.
Meanwhile, melt butter in a saucepan over medium heat, then stir in coconut milk and keep warm over low heat. Spoon 1 cup batter into coconut milk mixture and stir to combine, then pour mixture into remaining batter, add shredded coconut and fold to combine. Spoon into cupcake cases and bake until golden brown, and centres spring back when gently pressed (10-12 minutes). Cool on a wire rack, then serve topped with a dollop of passionfruit curd.