Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a large bowl, combine the flour, sugar, baking powder, and salt.
In a separate bowl, mix together the milk, melted butter, vanilla extract, and beaten egg.
Add the wet ingredients to the dry ingredients and stir until just combined.
Pour the batter into the prepared cake pan.
In a small bowl, mix the brown sugar and cinnamon. Sprinkle evenly over the batter.
Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool for a few minutes before serving.