Preheat your oven to 350°F (177°C). Grease a 9×13-inch (23 x 33 cm or 13 cup or 3.3 L) baking dish and line with parchment paper, letting the excess hang over the sides (you’ll use this to pull the cake out of the pan). Set aside.
In the bowl of an electric mixer (see note below recipe) fitted with the paddle attachment, cream butter, sugar, vanilla and cinnamon on medium speed for about 5-6 minutes or until light and fluffy. You want it pretty fluffy, so if your kitchen is chilly let the machine run longer. Scrape down the sides and bottom of the bowl to make sure everything is combined.
Add in the eggs, one at a time, making sure the first is well blended before adding in the second. Add the baking powder, baking soda and salt and mix for 1 minute more. Scrape the sides and bottom of the bowl to make sure everything is well blended.
In a liquid measuring cup (or medium bowl) whisk together the milk and sour cream. Alternate adding the flour and milk mixture in two batches, mixing each addition until just combined. Grab a spatula and scrape the sides and bottom of the bowl one more time to make sure the cake batter is thoroughly mixed.