Start by preheating the oven to 350F and lining 14 mini cupcake tins with cupcake liners. Set aside.
In a small bowl mix the flour, baking powder and the salt together and set aside.
In a medium bowl, mix the granulated sugar, egg white, and oil together until incorporated then add in the milk, the lemon zest and the water. Mix one more time until combined.
Divide the batter evenly between 14 cupcake liners and bake for 9 minutes.
For the lemon curd- As the cupcakes are baking, we will make the lemon curd.
In a medium saucepan, whisk the lemon juice, lemon zest, sugar and egg yolks over medium-low heat. Once the mixture starts to thicken remove it from the heat.( the time will depend on the temperature of your ingredients)
Add in the cubed butter and quickly whisk it in. (I usually use a hand blender to make my life easier.)
Place the lemon curd in a shallow bowl and cover it with plastic wrap making sure it touches the curd. This will keep it from forming a film on top. Let the curd cool completely in the fridge to thicken.