Preheat the oven to 325 degrees F/165 C. Grease the bottoms of the cake pans and then line them with a round of parchment paper.
In a small bowl, whisk together the oil and about half of the milk.
Add the flour, sugar, baking powder, and salt to a 5-quart mixing bowl and mix on low with the paddle until combined.
Add the cubed butter to the mixing bowl and mix on low until it's crumbly and looks like coarse sand.
With the mixer running on low, stream in the milk and oil mixture.
Increase to medium speed and mix for exactly 2 minutes.
Then whisk together the eggs, vanilla, and the rest of the milk.
With the mixer running on low, slowly stream the egg mixture into the bowl until combined. Scrape down the sides and bottom of the bowl, then mix for another 10-20 seconds until everything is homogenous.
Add the rainbow sprinkles and fold them gently into the batter with a rubber spatula.
Evenly distribute the batter into the prepared pans, it's best to do this with a scale. Each pan should have about 500 grams of batter.
Smooth the batter with a small offset spatula to fill the pans, then bake them for about 25 minutes or until the tops bounce back when touched.
Let the pans cool for 5 minutes on a cooling rack. The cake should start to pull away from the sides of the pans as they cool. Carefully knock out each layer and then let them cool competely on the rack.