Preheat oven to 350°F (175°C).

Sift flour 3 times.

In a large bowl, mix flour, brown sugar, granulated sugar, and cinnamon.

Add oil and mix well to form a crumbly mixture.

Reserve 3/4 cup of the mixture for topping.

Add nuts and cinnamon to the reserved topping mixture and set aside.

In a separate bowl, whisk together egg and sour milk or buttermilk.

Add the wet ingredients to the remaining cake mixture.

Add baking soda and baking powder to the cake mixture.

Beat well by hand until smooth.

Grease a 9 or 12-inch baking pan.

Pour the batter into the prepared pan.

Sprinkle the topping evenly over the batter.

Bake in the preheated oven for 35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let cool in the pan before slicing and serving.