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

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

Add the large eggs, one at a time, mixing well after each addition, then pour in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon.

Gradually add the dry ingredients to the butter mixture, alternating with the sour cream.

If desired, gently fold in the chopped nuts into the cookie dough.

In another bowl, combine the brown sugar, all-purpose flour, and ground cinnamon for the crumb topping.

Drop approximately 2 tablespoons of cookie dough onto the prepared baking sheets, spacing them about 2 inches apart.

Evenly sprinkle the prepared crumb topping onto each mound of cookie dough.

Bake for 12-15 minutes, until the edges are golden brown.

Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to wire racks.