Preheat the oven to 350 F. Line your muffin pans with paper liners - you'll need 18-20 liners.If you only have 1 pan, you can bake the first batch of 12 cupcakes and let the rest of the batter rest at room temperature until the pan is free to bake the second batch.
In a measuring cup, stir together the lemon juice and milk; set aside for a few minutes to let the milk curdle.
Measure the sugar into a large bowl, and zest the lemon over the sugar. Use your fingers to rub the lemon zest into the sugar to really infuse the lemon flavor.
Set a fine mesh strainer over the sugar, and sift in the flour, baking powder and salt, then whisk together the dry ingredients with the lemon sugar.
In a separate bowl, whisk together the lemon juice/milk mixture, eggs, egg white, sour cream, oil, melted butter, vanilla and lemon extracts until smooth. Add the wet ingredients to the dry and whisk by hand until smooth, about 30 seconds.
Use a 1/4 cup measuring cup to scoop the batter into the pan, filling the cups no more than 2/3-3/4 full.
Bake on the center oven rack for about 15-16 minutes, until the tops spring back when gently touched. Cool in the pan for 5 minutes, then gently transfer the cupcakes to a cooling rack to cool completely before frosting.