Preheat the oven to 350°F and grease and line three 6 inch cake tins with parchment paper. Set aside.
In a medium sized bowl, combine the flour, baking powder, baking soda, and salt. Whisk together to combine and set aside.
In a small bowl, combine the lemon juice and milk together. Letting these sit while you prepare the other ingredients allows the milk to curdle, which is good. Set aside and prepare the other ingredients.
In a large bowl (or in the bowl of a stand mixer), add the butter, oil, sudar, and lemon zest. Beat with a hand mixer (or with the paddle attachment if you are using a stand mixer) on high for 3-4 minutes or until light and fluffy. This creams the butter and sugar together while extracting the lemon flavors from the zest.
Next, add the eggs. Add each egg one at a time, mixing to fully incorporate the egg before adding the next. After the eggs are combined, add in the vanilla.
Now, add 1/3 of the flour mixture to the large bowl, beating on low speed until just combined. Add in 1/2 of the lemon and milk mixture, and beat until just combined. Add in another 1/3 of the flour mixture, and again beat until just combined. Add the last half of the lemon and milk mixture, beat in until combined. And finally, add in the last 1/3 of the flour mixture. Beat until just combined and no streaks of flour remain.
Once all of the ingredients are added, take a rubber spatula and fold the batter in on itself a couple of times, gently so as not to knock any air from the batter. Make sure to scrape the bottom of the bowl and mix the batter closer to the bottom with the batter from the top. This ensures that all ingredients are evenly distributed throughout the batter.
Evenly distribute the batter amongst the cake pans and bake in the preheated oven for 40-50 minutes, or until a toothpick inserted in the center of the cake comes out clean.
Once fully baked, remove from the oven and allow to cool before removing from the cake pans.