Preheat your oven to 350 degrees F and grease an 8×8 baking pan.
In a small bowl, combine 1/2 cup flour, brown sugar, and cinnamon for the topping.
Cut in 1/4 cup butter using a fork or pastry blender until crumbly.
Stir in the pecans and set aside.
In a large bowl, cream together the 1/2 cup butter and granulated sugar until fluffy.
Add the egg, sour cream, milk, and vanilla extract, mixing until smooth.
Whisk the dry ingredients (1 cup flour, salt, baking powder, baking soda) together then fold into the wet mixture.
Spread half the batter into the prepared pan.
Sprinkle half the crumble mixture over the batter.
Top with remaining batter and the remaining crumble.
Bake for 40-50 minutes or until a toothpick comes out clean.