Preheat the oven to 350 degrees and grease a 9x9 baking dish.
Beat butter and sugar until light and fluffy.
Add eggs, one at a time, beating after each addition. Scrape sides and bottom of the bowl.
Add vanilla and sour cream. Beat until well combined.
Sift in the flour, baking powder, baking soda, and salt. Beat on low speed until just mixed.
Scrape sides and bottom of the bowl, and coconut. Fold until incorporated throughout.
Pour batter into prepared baking dish and spread it evenly.
Crumble: In a medium bowl, combine brown sugar, white sugar, and flour. Mix well until all ingredients are incorporated evenly.Pour in melted butter, and carefully fold it in with a large fork. You will want to be careful so you don't overmix. Streusel should look like large crumbs and not paste. Add coconut flakes and carefully fold them in.
Sprinkle crumble topping over batter evenly.
Bake for 55-60 minutes and do a toothpick test in the center to make sure it's done. Cool to room temperature before cutting.
Recipe from Lyuba @ willcookforsmiles.com All images and content are copyright protected. Please do not use my images without prior permission. If you want to share this recipe, please simply link back to this post for the recipe. Thank you.