You’ll need:
For the coconut mixture:
6 ounces coconut (about 1 1/4 cups)
1/2 cup brown sugar sugar
1 tablespoon ground cinnamon
For the cake:
2 cups all-purpose flour, plus more for coating the pan
1 1/2 teaspoons baking powder
1 1/2 teaspoons baking soda
1/2 teaspoon fine salt
2 sticks (8 ounces) unsalted butter, at room temperature, plus more for coating the pan
1 1/4 cups granulated sugar
2 large eggs, at room temperature
1 cup sour cream, at room temperature
1 1/2 teaspoons vanilla extract
For the coconut mixture:
Mix all of the ingredients together; set aside.
For the cake:
Heat the oven to 325°F and arrange a rack in the middle. Coat a 9-by-9-inch metal baking pan with butter and dust with flour, tapping out the excess; set aside. Sift the measured flour, baking powder, baking soda, and salt into a medium bowl and set aside.
Place the butter and sugar 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 eggs 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 the sour cream and vanilla, 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.