Line your 12 cup standard muffin tin with 9 paper liners.
Preheat your oven to 350℉.
In the bowl of a standing mixer place the granulated sugar and lemon zest. Mix on low speen for 1-2 minutes.
Next add the flour, baking powder and kosher salt. Mix on low for 30 seconds.
With the mixer running on low, add the butter in small pieces. MIx until the mixture looks like sand. This should take about 2-3 minutes.
In a seperate bowl, whisk together the milk, oil, whole egg and egg yolk.
With the mixer running on low, gradually add the liquid ingredients. Once all the liquid has been added turn the mixer up to medium speed(6) and mix for 45 seconds. Scrap the bottom and sides of the bol and mix at medium speed for an additional 15 seconds. The mixture should be smooth with no lumps.
Divide the batter evenly amongst the 9- cupcake liners.
Bake the cupcakes for 18 minutes.
Allow the cupcakes to cool completely then remove them from the pan.
