In a large mixing bowl, add flour, sugar, baking powder, baking soda and nutmeg.
Whisk together to combine.
Add butter to bowl.
Using a pastry blender, cut butter into flour mixture until it resembles coarse crumbs.TIP: You'll still want to see pea sized pieces of butter within the flour mixture. When the butter melts while baking, it will make for a light and airy cake.
Add buttermilk, eggs and vanilla to bowl.
Stir together until just combined.
In a small bowl, add mango and flour
Stir together until mango is evenly covered with flour.TIP: Coating the fresh fruit in a thin layer of flour insures that the mango will not sink to the bottom of the cake, rather it will stud the entire cake instead.
Add mango to bowl of coffee cake batter. Stir together until just combined.
Pour batter into greased 9″ x 13″ baking dish.
Cinnamon Sugar Topping
In a small bowl, add cinnamon and sugar.
Stir together to combine.
Sprinkle in an even layer over coffee cake batter.TIP: Once baked, the cinnamon sugar layer provides a crunch to an otherwise soft and airy cake. A great contrast in texture!
Bake for 45 minutes or until golden and toothpick inserted into center removes cleanly.