Preheat oven to 350°F. Spray two 9-inch cake pans with cooking spray (I use coconut oil spray), then line with unbleached parchment paper, then spray the parchment paper before pouring the cake batter in the pans. This method will prevent sticking.
In a medium bowl, combine flour, salt, baking powder, and baking soda, whisk slightly. Set flour mixture aside.
With a mixer fitted and the whisk attachment, beat the room temperature butter and sugar together on high speed until smooth and creamy (2-3 minutes) scraping down the sides as needed.
Beat in the four eggs and vanilla extract on medium speed till incorporated, then turn up to high speed until combined, about 2 minutes (don't worry if the batter looks curdled) scraping down the sides as necessary.
Next, slowly combine the dry ingredients with the wet mixture until combined but no longer. Then, with the mixer continuing to run on the lowest speed, pour in the milk and mix just until combined. Check that there are no lumps at the bottom of the bowl and scrape well to make sure the batter is smooth - just don't overmix it.
Dived the batter evenly into six portions, then pour batter into prepared cake pans. I use a scale. If you only have two cake pans, you might need to do three sets of cakes. (this is what I do!)
Bake for around 12-14 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake. If it comes out clean, it's done. Allow cakes to cool completely in the pans on top of wire racks, then flip out carefully before assembling.
Using the filling, spread equal portions between cake layers, stacking as you go until you've used all the cakes. Time to make the glaze!