Preheat and Prep:
Preheat the oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan and set aside.
Cream Butter and Sugar:
In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy using a hand or stand mixer.
Add Wet Ingredients:
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract until fully combined.
Mix Dry Ingredients:
In a separate bowl, whisk together the flour, baking powder, salt, and ground cinnamon.
Combine Wet and Dry:
Gradually add the dry ingredients to the creamed mixture, alternating with the milk. Mix until just combined—do not overmix.
Make Cinnamon Swirl:
In a small bowl, mix together the brown sugar and walnuts (if using) for the swirl layer.
Layer and Swirl:
Pour half of the cake batter into the prepared pan and smooth the surface. Sprinkle half of the brown sugar mixture evenly over the batter. Add the remaining batter and top with the rest of the cinnamon sugar mixture. Use a knife to gently swirl the layers together.
Bake:
Bake for 30–35 minutes or until a toothpick inserted into the center comes out clean and the top is golden brown.
Cool and Serve:
Allow to cool in the pan for 10 minutes before slicing. Serve warm or at room temperature.
