Preheat your oven to 350°F and grease a 9x13-inch baking dish.

In a large bowl, cream the butter and sugar together until light and fluffy.

Beat in the eggs, one at a time, then add the vanilla extract.

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

Add the dry ingredients to the butter mixture alternately with the sour cream, starting and ending with the flour mixture. Stir until just combined.

Gently fold in the chopped peaches.

Spread the batter evenly into the prepared baking dish.

In a small bowl, mix the brown sugar, pecans (if using), cinnamon, and flour. Cut in the cold butter until the mixture is crumbly.

Sprinkle this mixture evenly over the batter.

Bake for 40–45 minutes or until a toothpick inserted in the center comes out clean.

Let cool slightly before slicing and serving warm.