Preheat your oven to 350-375°F and grease a 9x13 inch cake pan.
In a mixing bowl, combine baker's flour, brown sugar, granulated sugar, salt, nutmeg, and salad oil until crumbly.
Reserve 1/2 cup of the mixture for topping and mix in cinnamon.
In another bowl, blend together baking soda, baking powder, egg, and buttermilk.
Gently fold the wet mixture into the dry ingredients until just combined.
Pour the batter into the greased cake pan.
Sprinkle the reserved cinnamon crumb topping evenly over the batter.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.