Preheat the oven to 350°F (177°C). Butter and flour three 6" cake pans and put a circle of parchment paper at the bottom of each pan. If you're using cake strips, you can add them now.
Combine the dry ingredients (flour, baking powder, salt, and cinnamon) in a bowl and set aside.
In a stand mixer or using a hand held mixer, beat the butter on medium (4) speed for 3-4 minutes until it is fluffy and lighter in color. Scrape down the sides.
Add brown and white sugar and beat on medium (4) speed for 2 minutes. Scrape down the sides of the bowl.
Add the vanilla to the eggs.
Slowly add the eggs one at a time on low (2) speed and then increase the speed to medium (4) after each egg for about 30 seconds. After the last egg, beat the mixture on medium (4) for 1 minute. Scrape down the sides of the bowl.
On low (1) speed, slowly add the half of the dry ingredients. Then immediately add half of the milk.
Add the remaining dry ingredients and then the remaining milk mixture. Barely mixing it as this point. Be careful not to overmix. Stop the mixer and use a rubber spatula to gently make sure the cake batter is all incorporated.
Bake for 25-30 minutes or until the centers are done. The cake is done when you insert a toothpick into the center and it comes out clean.
Let it cool completely on cooling rack before removing from the pans.