Preheat the oven to 350°F. Grease a 9-inch cake pan with butter or cooking spray.
In a large mixing bowl, cream together the butter and sugar until light and fluffy.
Add in the eggs, one at a time, mixing well after each addition.
In a separate bowl, whisk together the flour, baking powder, cinnamon, and salt.
Gradually add the dry ingredients to the butter mixture, alternating with the milk, and mix until just combined.
Pour the batter into the prepared cake pan and smooth out the top with a spatula.
In a small bowl, mix together 1/4 cup granulated sugar and 1 teaspoon ground cinnamon. Sprinkle the cinnamon sugar mixture evenly over the top of the batter.
Bake the cake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool for a few minutes before slicing and serving.