Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking dish or line it with parchment paper for easy removal.
2. Make the Cake Batter:
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, beat together the butter and granulated sugar until light and fluffy, about 2-3 minutes.
Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk. Start and end with the dry ingredients. Mix until just combined, being careful not to overmix.
3. Prepare the Cinnamon Swirl:
In a small bowl, combine the melted butter, brown sugar, and cinnamon. Stir until smooth and well combined.
4. Assemble the Cake:
Pour the cake batter into the prepared baking dish and spread it evenly with a spatula.
Drizzle the cinnamon swirl mixture over the top of the cake batter. Use a knife or toothpick to swirl the cinnamon mixture through the batter in a zigzag pattern. The swirl should be evenly distributed but not fully mixed into the batter.
5. Bake the Cake:
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean (a few moist crumbs are okay, but it shouldn’t be wet).
If the cake begins to brown too quickly on top, cover it loosely with aluminum foil and continue baking.
6. Make the Glaze:
While the cake is baking, whisk together the powdered sugar, milk, and vanilla extract in a small bowl until smooth. Add more milk if needed to reach your desired consistency (the glaze should be pourable but not too runny).
7. Finish the Cake:
Once the cake is done, remove it from the oven and allow it to cool for about 10 minutes in the pan.
Drizzle the glaze over the warm cake, allowing it to soak in and create a sweet, glossy finish.
8. Serve:
Serve the cake warm or at room temperature. It’s delicious on its own, or you can serve it with a scoop of ice cream or a dollop of whipped cream for extra indulgence.
