Preheat your oven to 180C 356F or 160C (320F) for a fan forced oven. Line a cupcake tin with cupcake liners.
In the bowl of a stand mixer fitted with the paddle attachment, add the flour, baking powder, caster sugar and salt. Turn mixer on low speed and allow it to mix for a couple minutes to help everything combine well (alternatively you may do this by sifting the ingredients together). Add the softened butter and let it mix until it resembles a fine sand like texture.
Next, add milk, eggs, yogurt, oil and vanilla extract in a large jug and whisk well.
Add wet ingredients to dry ingredients in a slow and steady stream until no dry ingredients are visible. Scrape down the bowl, add fresh zest of one lemon, and mix for another 20 seconds.
Fill each cupcake liner 3/4 of the way (using an ice cream scoop to transfer the batter into the cupcake liners makes this a quick and easy process otherwise you can use two tablespoons). Bake for 20-25 min or until a toothpick inserted comes out clean. Allow them to cool completely on a wire cooling rack before frosting.
Place about an inch of water to a medium sized pot and bring it to the boil.
Add your egg whites, sugar and cream of tartar to a large, clean metal bowl. Mix using a whisk or hand held mixer to help combine all the ingredients.
Place the bowl with the egg mixture on top of your pot of boiling water making sure the bottom of the mixing bowl doesn’t touch the bottom of the pot. Mix on high speed for 5 min or until the sugar in the mixture completely dissolves. You can check this by dipping two (clean) fingers into the mixture and if you can’t feel any grains of sugar it’s ready to take off the pot. Mix on high speed once you’ve taken it off the heat (about 5-6 min) until the mixture cools down and gets thick and glossy. You want to reach stiff peaks so that the frosting holds it’s shape well.
To finish off the cupcakes core each one and fill the centre with lemon curd. Fit the end of a piping bag with an open star tip and frosting in a swirl motion as demonstrated in the video. Use a kitchen torch to toast the frosting right before serving and top it with some crushed pie crust.
Cupcakes can be stored in an airtight container for up to three days.