Preheat your oven to 350°F (175°C). Grease a 9x9-inch baking pan.
Make the crumb topping: Mix flour, brown sugar, and cinnamon. Add melted butter and stir until crumbly.
For the cake batter: Whisk together flour, sugar, baking powder, baking soda, and salt in a large bowl.
In another bowl, beat eggs, milk, and vanilla extract.
Combine wet and dry ingredients, mixing until just blended.
Pour batter into the prepared pan. Sprinkle crumb topping evenly over the batter.
Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan before dusting with powdered sugar and serving your Copycat Entenmann's Coffee Cake.