Add the flour, brown sugar, and cinnamon to a large mixing bowl and whisk until well combined. Add the cubed cold butter and cut it into the mixture with a pastry blender or a fork until the mixture starts to come together and is crumbly. Transfer to the refrigerator until ready to use.
Preheat the oven to 350°F (177°C). Spray a 9-inch springform pan with non-stick cooking spray and set aside.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a handheld mixer, beat the butter, granulated sugar, and brown sugar together until light and fluffy (about 4-5 minutes). Mix in the eggs one at a time until fully incorporated, then mix in the vanilla extract, stopping to scrape down the sides of the bowl as needed.
With the mixer on low speed, add the dry ingredients in three parts alternating with the buttermilk (starting and ending with the flour). Make sure to mix each addition until just combined.
Gently fold in the chopped apples until well incorporated into the cake batter.
Scoop the batter into the prepared springform pan and smooth it out evenly. Remove the crumb topping from the refrigerator and sprinkle it evenly over the top.
Bake for 45 to 55 minutes (mine is usually perfect at 50 minutes) or until a toothpick inserted into the center comes out clean. If needed, cover loosely with foil around the 40-minute mark to prevent excess browning.
Remove the cake from the oven and cool on a wire rack for at least 20 to 30 minutes before releasing it from the springform pan. Allow to cool completely, then slice and enjoy!
