Step 1: Prepare Your Oven and Pan

Preheat your oven to 350°F (175°C). Generously grease a 9×13-inch baking pan with butter or non-stick spray, then dust lightly with flour, tapping out any excess. Alternatively, line the bottom with parchment paper for easier removal. This step is crucial for preventing sticking and ensuring your beautiful cake comes out in one piece!

Step 2: Mix the Dry Ingredients

In a large mixing bowl, whisk together the flour, baking powder, baking soda, and salt until well combined. This distributes the leavening agents evenly throughout the flour, ensuring your cake rises uniformly. Set this bowl aside while you prepare the wet ingredients.

Step 3: Cream the Butter and Sugar

In another large mixing bowl (or the bowl of your stand mixer), beat the softened butter and granulated sugar together on medium-high speed for 3-4 minutes until light, fluffy, and pale in color. This creaming process incorporates air into the batter, which helps create a lighter, more tender cake. Scrape down the sides of the bowl as needed to ensure even mixing. The mixture should look almost white and have increased in volume.

Step 4: Add Eggs and Vanilla

Add the eggs one at a time, beating well after each addition (about 30 seconds per egg). Make sure each egg is fully incorporated before adding the next. Add the vanilla extract and beat until combined. The mixture might look slightly curdled at this point – that’s completely normal and will come together once you add the dry ingredients.

Step 5: Alternate Dry and Wet Ingredients

With your mixer on low speed (or mixing gently by hand), add the flour mixture in three additions, alternating with the sour cream and milk in two additions. Start and end with the flour mixture. The pattern should be: flour, sour cream/milk, flour, sour cream/milk, flour. Mix just until each addition is incorporated – don’t overmix or you’ll develop too much gluten and end up with a tough cake. A few small lumps are fine. The batter should be thick, smooth, and creamy.

Step 6: Make the Cinnamon Swirl Mixture

In a small bowl, combine the sugar, cinnamon, and melted butter. Mix with a fork until it resembles wet sand. This mixture creates those beautiful ribbons of cinnamon throughout your cake.

Step 7: Layer and Swirl

Spread half of the cake batter into your prepared pan, smoothing it into an even layer with your spatula. Sprinkle half of the cinnamon-sugar mixture evenly over the batter. Don’t worry about covering every inch – gaps are fine! Use a butter knife or offset spatula to gently swirl the cinnamon mixture into the batter, creating a marble pattern. Don’t over-swirl or you’ll lose the distinct layers. Spread the remaining batter on top and smooth it out. Sprinkle the remaining cinnamon mixture over the top and swirl again, creating those gorgeous patterns.

Step 8: Bake the Cake

Place the pan in the preheated oven and bake for 38-45 minutes, until the top is golden brown and springs back when lightly touched. A toothpick inserted into the center should come out clean or with just a few moist crumbs (but no wet batter). The exact baking time depends on your oven and pan – start checking at 38 minutes. The edges will pull slightly away from the pan when done.

Step 9: Cool the Cake

Remove the cake from the oven and place the pan on a cooling rack. Let it cool in the pan for about 15-20 minutes. This cooling period allows the cake to set properly – if you try to remove it too soon, it might break apart. After 15-20 minutes, you can either leave it in the pan to cool completely (my preference for easier serving) or carefully turn it out onto a cooling rack.

Step 10: Make the Glaze

While the cake cools, make the vanilla glaze. In a medium bowl, whisk together the sifted powdered sugar, 3 tablespoons of milk, vanilla extract, and a pinch of salt until smooth. The glaze should be pourable but not too thin – it should coat the back of a spoon. If it’s too thick, add more milk one teaspoon at a time. If too thin, add more powdered sugar.

Step 11: Glaze and Serve

Once the cake has cooled for at least 20-30 minutes (it should be warm but not hot), drizzle the glaze over the top using a spoon or pour it from the bowl. Use a spatula to spread it if desired, or let it drip naturally for a rustic look. The glaze will set as it cools. Let the glaze set for about 10 minutes before slicing and serving. Cut into squares and enjoy!