In a medium bowl, sift together the flour, baking powder, baking soda, kosher salt, cinnamon, and nutmeg.
2 (250 g) cups All purpose flour, 1 ½ teaspoon Baking powder, ½ teaspoon Baking soda, ½ teaspoon Kosher salt, 2 teaspoons Ground cinnamon, ½ teaspoon Ground nutmeg
Peel and grate 1 apple into a bowl. After grating, using paper towels or a linen towel, squeeze the apples by hand until they have released all of their liquid. After draining, measure 1 cup of the shredded and drained apples. (This was about one medium apple for me.)
1 cup Grated apples
In a stand mixer fitted with the paddle attachment, beat the softened butter and sugars together on low speed for 1 ½ minutes until combined. Scrape the bowl then increase the mixer to medium speed and beat for an additional 1 ½ minutes until light and fluffy. Scrape down the sides of the bowl and the paddle.
6 (84 g) tablespoons Unsalted butter, ½ (100 g) cup Granulated sugar, ½ (110 g) cup Light brown sugar
On low speed, add the eggs one at a time, until each one is incorporated and the mixture is light and fluffy. Next, add in the applesauce and vanilla extract and mix on medium speed until combined. Scrape down the sides of the bowl and the paddle. (The mixture may look a little broken at this point but it will come back together.)
2 large Eggs, 2 (30 g) tablespoons Unsweetened applesauce, 1 tablespoon Vanilla extract
With the mixer on low, add ⅓ of the flour mixture and mix until just combined. Scrape the bottom and sides of the bowl with a rubber spatula. If still you see a little specs of flour its ok. Next, add in half of the sour cream and mix on low until just combined. Scrape the sides and bottom of the bowl. Add in another ⅓ of the flour mixture, repeating the same steps as above. Add the last half of the sour cream, mixing until just combined. Scrape the sides and bottom of the bowl. Add the last of the flour and mix until almost incorporated. Add the grated apples and mix the rest of the batter by hand with a rubber spatula. Be careful not to over-mix.
½ (120 g) cup Sour cream
Pour the batter into the prepared loaf pan. Tap the pan a few times on the counter to release the air bubbles then smooth the top of the batter with an offset spatula until smooth. Top the batter with the streusel topping and gently press down so it adheres.
Bake at 350℉ for 55-60 minutes, or until a wooden skewer or cake tester comes out clean or with a few moist crumbs. Allow the bread to cool in the loaf pan on a wire rack for 10 minutes, then using the parchment overhang, lift the bread from the pan and onto a wire rack to cool completely.