Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a mixing bowl, combine the flour, sugar, baking powder, baking soda, and salt.
Add the buttermilk, melted butter, and eggs. Mix until smooth.
Pour the batter into the prepared baking pan.
In another bowl, mix together the brown sugar, flour, melted butter, and cinnamon for the crumb topping.
Sprinkle the crumb topping evenly over the batter.
Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center comes out clean.
Let cool before serving. Enjoy!