Preheat oven to 350 degrees (325 if you have a dark-coated pan). Line 9x13 pan with parchment paper. Set aside.
Add flour, baking powder, baking soda, cinnamon, and salt to a medium bowl. Whisk together to combine. Set aside.
Add butter and sugar to the bowl of a stand mixer. With a paddle attachment, beat together until nice and creamy, about 2-3 minutes. Add eggs one at a time, mixing until combined. Scrape down the sides of the bowl to make sure it's all mixed together. In a measuring cup, whisk sour cream and milk together. Set aside.
Add 1/3 of flour mixture to butter mixture and mix just until it's somewhat combined. Add 1/2 sour cream mixture and mix until combined. And second 1/3 of flour mixture and mix until combined. Add remaining sour cream mixture and mix until combined. Finally, finish with the last 1/3 of flour mixture and mix until combined.
Add 3/4 cup chocolate chips and fold into mixture until evenly dispersed. Spread mixture into prepared pan and cover with streusel topping. Sprinkle remaining 1/2 cup of chocolate chips on the top.
Bake in preheated oven for about 30-40 minutes, or until toothpick comes out clean when inserted in the center. Let it cool for at least 10 minutes before serving. Enjoy!