need sour cream, double the topping part.
16 tbsp. unsalted butter, melted,
plus more for the pan
3 3/4 cups flour, plus more for pan
1 1/4 cups plus 2 tsp. sugar
6 tbsp. plus 1 1/2 tsp. packed light
brown sugar
2 tbsp. plus 1/2 tsp. ground cinnamon
1 1/4 tsp. kosher salt
1/3 cup finely chopped pecans
2 1/2 tsp. baking powder
1 cup milk
6 tbsp. sour cream
2 1/4 tsp. vanilla extract
1 1/2 tsp. cinnamon extract
2 eggs
1. Heat oven to 325°. Grease an 8" x 8" baking pan with a little butter and sprinkle with a little flour; set aside. Make topping: In a bowl, mix 8 tbsp. melted butter, 1/4 cup sugar, 6 tbsp. brown sugar, 2 tbsp. ground cinnamon, and 1/2 tsp. salt until smooth. Add 1 1/2 cups flour; mix with a fork until crumbly; chill. Make filling: In a bowl, mix remaining brown sugar, 2 tsp. sugar, 1/2 tsp. ground cinnamon, and pecans; set filling aside.
2. Make cake batter: In another bowl, whisk together remaining flour, sugar, salt, and baking powder; set aside. In a large measuring cup, whisk together remaining butter, milk, sour cream, vanilla, cinnamon extract, and eggs until smooth. Pour wet ingredients over dry ingredients; whisk to combine. Pour half the batter into prepared baking pan. Sprinkle filling over top; pour remaining batter over it. Break up reserved topping with fingers; sprinkle over top; bake until a toothpick inserted into middle of cake comes out clean, about 1 hour 15 minutes. Let cool before serving.
http://www.saveur.com/article/Recipes/Cinnamon-Coffee-Cake