Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

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

Incorporate the eggs one at a time, then mix in the vanilla extract until smooth.

Whisk together the dry ingredients: flour, baking powder, baking soda, salt, and cinnamon in a separate bowl.

Gradually combine the dry mixture with the wet ingredients, mixing on low speed.

Fold in the sour cream until the dough resembles a thick batter.

If using, fold in the chopped nuts evenly into the dough.

Prepare the crumb topping by mixing brown sugar, flour, and cinnamon, then cut in cold butter until crumbly.

Scoop heaping tablespoons of dough onto the prepared baking sheets, leaving space between each scoop.

Sprinkle the crumb topping over each cookie mound, pressing lightly to adhere.

Bake for 12-15 minutes until edges are golden and centers are soft. Let cool for 5 minutes on sheets.