Preheat oven to 350F (175C). Lightly grease and flour the sides and bottoms of three 8” round baking pans. Set aside.
In a large bowl (or the bowl of a stand mixer) whisk together flour, sugar, baking powder, and salt until well-combined.
Using an electric mixer on low speed, add butter one tablespoon at a time. Do not add the next tablespoon until the first has been fully incorporated. Mixture should resemble sandy, coarse crumbs.
Add the oil and stir on low-speed until all of the dry ingredients have been moistened.
In a separate bowl (I use a large measuring cup) whisk together buttermilk, eggs, and vanilla extract until well combined.
With mixer on low-speed, gradually pour milk mixture into flour mixture. Once combined, scrape down the sides and bottom of the bowl using a spatula. Stir once more until batter is uniform and smooth.
Evenly divide cake batter into prepared pans and prepare cinnamon swirl.
In a small bowl, whisk together sugar and cinnamon for cake swirl.
Sprinkle a heaping Tablespoon of cinnamon/sugar over each cake layer. Use a butter knife to swirl the mixture into the cake batter.
Transfer cakes to center rack of 350F (175C) oven and bake for 28-30 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Allow cakes to cool for 15 minutes and then invert onto a cooling rack to cool completely before frosting.
In a large mixing bowl, combine cream cheese, butter, and brown sugar and use an electric mixer to beat until smooth and creamy.
Add ground cinnamon, vanilla extract and salt, stir until combined.
With mixer on low speed, gradually add powdered sugar until frosting is smooth and creamy.
If cakes are domed or unlevel, level cakes before assembly. I do thin layers of frosting between cake layers, a semi-naked frosting around the cake, and then decorative swirls on top using an Ateco 846 or 848 tip.