Preheat your oven to 350°F (180°C). Lightly grease the bottoms of three 8-inch cake pans and line each bottom with a round piece of parchment paper. In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon; set aside. (3½ cups/420 g all-purpose flour, 2 tsp baking powder, ¾ tsp baking soda, 1 tsp salt, 2 tsp cinnamon) In a stand mixer bowl, cream the butter, sugar, and oil together for about 3 minutes until the mixture is light and fluffy. (¾ cup/170 g unsalted butter at room temperature, ¼ cup/50 g canola oil, 1½ cups/300 g granulated sugar) Add the eggs one at a time, beating well after each addition until fully incorporated. Be sure to scrape down the sides and bottom of the bowl. (3 large eggs, room temperature) Stir in the vanilla extract and sour cream. (1 tbsp vanilla, ¼ cup/60 g sour cream or Greek yogurt, room temperature) Add one-third of the dry ingredients and mix until nearly combined, then pour in half of the buttermilk. Continue alternating between the remaining dry ingredients and buttermilk, mixing until everything is just combined. Scrape the bowl to ensure an even mix. (1¼ cups/285 g buttermilk, room temperature) Divide the batter evenly among the three prepared pans, approximately 471 grams per pan. Bake on the middle rack for 18–20 minutes or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for 15 minutes, then run a spatula around the edges and invert them onto wire racks to cool completely.

In a stand mixer bowl, beat the cold cream cheese on medium speed until smooth. Add the unsalted butter and mix until well combined. (4 oz cold full-fat cream cheese, 1 cup/226 g unsalted butter) Gradually add the powdered sugar, about half a cup at a time, mixing on low speed after each addition. (2 cups/200 g powdered sugar) Add the milk and vanilla extract, mixing to combine. (1 tbsp 2% milk, 1 tsp vanilla extract) Increase the mixer speed to medium and beat for 30 seconds until the frosting is fluffy yet thick. Cover and refrigerate until ready to use. Before assembling, briefly beat the frosting for 20–30 seconds to soften it slightly, but avoid overmixing which can make it too wet.

Combine the cinnamon and sugar in a large bowl and set aside. (1 tsp cinnamon, ½ cup/100 g granulated sugar) Using a serrated knife, carefully trim the crust off the edges of each cake layer to reveal the crumb. Roll the sides of each layer in the cinnamon sugar mixture. If the sugar doesn’t stick well, brush the sides lightly with melted butter or simple syrup (see notes) before rolling to coat evenly. Place one cake layer onto your cake stand, platter, or a cardboard round. Spread ¼ cup of dulce de leche evenly on top of the layer, leaving a ½-inch border around the edges clear. (1 can dulce de leche) Fill a large piping bag fitted with a large round tip with the buttercream frosting. Pipe a “tire ring” about 1 inch tall around the edge of the cake layer, then pipe a loose zigzag layer of frosting over the dulce de leche in the center. Use a spatula to smooth only the center frosting to cover the dulce de leche, but do not smooth the outer tire ring border. Carefully place the next cake layer on top without pressing down to avoid pushing the frosting out of the sides. Repeat the process for all layers, finishing the top layer by piping dollops of frosting along half of the cake’s edge. Chill the assembled cake in the freezer for at least 20 minutes, or until the frosting has set. Once firm, remove and serve. Enjoy!