Preheat the steamer over high heat.
In a pot, cook water with pandan leaves and palm sugar until everything dissolves. Set aside.
In a mixer, combine egg yolks, granulated sugar, and vanilla extract over high speed until pale.
Add in pandan water, flour, baking powder, baking soda, and salt. Mix over low speed.
Add oil and mix the batter with a spatula.
Pour the batter into cupcake silicone molds and steam for 20 minutes over high heat. DO NOT open the lid while the cupcakes are cooking.