Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan.

Make the crumble topping: Mix melted butter, brown sugar, flour, cinnamon, and pecans (if using) in a bowl. Set aside.

Prepare the cinnamon sugar filling by combining brown sugar, flour, and cinnamon in a small bowl.

In a large bowl, cream softened butter, brown sugar, and granulated sugar until light and fluffy.

Beat in eggs one at a time. Stir in vanilla extract, sour cream, and sourdough discard.

In a separate bowl, whisk together flour, baking powder, and salt.

Alternate adding the dry mixture and buttermilk into the wet ingredients, mixing just until combined.

Pour half of the batter into the prepared pan. Sprinkle with the cinnamon sugar filling.

Spread the remaining batter on top and sprinkle with the crumble topping.

Bake for 45–50 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.

Let cool in the pan for 20 minutes before slicing and serving.