Mix together Sweetened Coconut Flakes (6 ounce), Brown Sugar (1/2 cup), and Ground Cinnamon (1 tablespoon), set aside.
Preheat oven to 325 degrees F (163 degrees C) and arrange a rack in the middle.
Grease a 9x9-inch metal baking pan with butter and then coat with a dusting of flour, tapping out the excess. Set aside.
Sift All-Purpose Flour (2 cup), Baking Powder (1 1/2 teaspoon), Baking Soda (1 1/2 teaspoon), and Fine Salt (1/2 teaspoon) into a medium bowl and set aside.
Place Unsalted Butter (2 stick) and Granulated Sugar (1 1/4 cup) in the bowl of a stand mixer fitted with a paddle attachment.
Beat on medium-high speed until lightened in color and fluffy, about 3 minutes.
Add the Egg (2) 1 at a time, letting the first completely incorporate before adding the second. Stop the mixer and scrape down the sides of the bowl and paddle with a rubber spatula.
Add Sour Cream (1 cup) and Pure Vanilla Extract (1 1/2 teaspoon), turn the mixer to medium speed, and continue beating until just incorporated, about 1 minute.
Stop the mixer and scrape down the sides of the bowl and paddle. Turn the mixer to low speed and slowly add in the flour mixture. Mix until just incorporated.
Spread half of the batter in the prepared pan. Sprinkle with half of the coconut mixture.
Dollop the remaining batter over the coconut mixture and spread into an even layer. Sprinkle with the remaining coconut mixture and gently press it into the batter.
Bake until a cake tester or toothpick comes out dry with a few crumbs attached, about 45 minutes.
Transfer the pan to a wire rack and let cool at least 20 minutes before serving. Enjoy!