Gather flour, sugar, butter, eggs, baking powder, vanilla extract, milk, and cinnamon for the cake and crumb topping.
Combine flour, sugar, baking powder, and cinnamon in a mixing bowl.
Mix in melted butter, eggs, vanilla extract, and milk until smooth.
In a separate bowl, mix flour, sugar, butter, and cinnamon until crumbly.
Pour half the cake batter into a greased pan and sprinkle with half of the streusel mixture.
Add the remaining batter and top with the rest of the streusel.
Let the cake cool before slicing and serving. Enjoy your homemade birthday crumb cake!