Step 1: Prepare the Oven and Pan
Preheat your oven to 350°F (175°C).
Grease a 9×13-inch baking pan with nonstick spray or butter. Set aside.

Step 2: Make the Cake Batter
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, mix the milk, eggs, and vanilla extract until combined.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Add the melted butter and mix until smooth and creamy.
Pour the batter evenly into the prepared baking pan.

Step 3: Prepare the Cinnamon Swirl
In a separate bowl, combine the brown sugar and cinnamon.
Add the softened butter and mix until a thick, crumbly paste forms.

Step 4: Add the Swirl to the Cake
Drop spoonfuls of the cinnamon mixture over the cake batter.
Use a knife or skewer to swirl the cinnamon mixture through the cake, creating a marbled effect.

Step 5: Bake the Cake
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Check at 35 minutes to avoid overbaking.

Step 6: Prepare the Glaze
While the cake bakes, whisk together the powdered sugar, milk, and vanilla extract until smooth.
Adjust the consistency by adding more milk for a thinner glaze or more powdered sugar for a thicker one.

Step 7: Glaze the Warm Cake
Once the cake is baked, remove it from the oven and immediately drizzle the glaze over the warm cake.
Allow the glaze to soak in, creating that classic cinnamon roll gooeyness.

Step 8: Serve and Enjoy
Let the cake cool slightly before slicing.
Serve warm for the best experience, but it’s just as delicious at room temperature!