Preheat the oven to 350F (180C). Line the bottom of your pans with rounds of baking paper and grease and flour the sides. I do not recommend just greasing and flouring the pan and omitting the paper, as the cakes are more likely to stick.
Whisk together the milk and lemon juice in a measuring jug or bowl. Set aside.
In a separate medium bowl, sift in the flour, baking powder, baking soda and salt. Whisk together. Set aside.
In a large bowl, beat together the butter, oil, granulated sugar and lemon zest until well creamed (about 2-3 minutes).
Add the vanilla into the butter mixture. Beat in the eggs 1 at a time. Turn off the mixer and scrape down the sides and bottom of the bowl after each addition.
Mix the dry ingredients and wet ingredients into the bowl of the butter mixture, alternating between additions. First, mix in 1/3 of the dry ingredients. Then mix in 1/2 of the milk and lemon juice mixture. Mix in another 1/3 of the dry ingredients, followed by the second 1/2 of the milk. Lastly, mix in the final 1/3 of the dry ingredients. Do not overmix. I always do a few stirs of each step by hand first. You may see pieces of lemon zest, but there shouldn't be lumps of flour.
Evenly distribute the cake batter between the prepared tins and smooth the tops. Bake in the middle of the preheated oven, with all the cake pans on the same rack, for about 20-25 minutes. When finished, the cakes should be starting to pull away from the sides of the pan and an inserted toothpick should come out clean or with a few crumbs, but no gooey cake batter.
Cool the cakes in the pans for at least 20 minutes before very carefully inverting onto cooling racks.