Preheat the oven to 350°F (175 ℃). Grease a 9×9 inch light metal baking pan and line it with parchment paper.
In a medium bowl, whisk together the flour, spices, baking powder, baking soda, and salt. Then set aside the flour mixture.
2 1/4 cups (282 g) all-purpose flour, spooned and leveled, 1 tbsp cinnamon, 1 tsp nutmeg, 1/2 tsp allspice, 1 1/2 tsp baking powder, 1/4 tsp baking soda, 1/2 tsp salt
To a large bowl add the softened butter, brown sugar and granulated white sugar. Cream together with an electric mixer on high speed for 2 minutes. (If using a stand mixer, use the paddle attachment.) 10 tbsp (140 g) unsalted butter, softened, 1 cup (220 g) light brown sugar, 1/2 cup (100 g) granulated white sugar
Then add in the eggs and vanilla. Mix on medium speed until pale in color and smooth, about 1 minute.
3 eggs, at room temperature, 1 tbsp vanilla
Add in the buttermilk and sour cream. Mix on medium speed until combined. (The batter will look split at this point, but don't worry. It will pull together once the dry ingredients are added in.)
2/3 cup (160 ml) buttermilk, at room temperature, 1/3 cup (82 g) sour cream, at room temperature
Add in the dry ingredients, mixing on low speed until all is combined and the batter is smooth. Scrape the sides of the bowl with a rubber spatula as necessary.
Pour half of the cake batter into the prepared baking pan. Smooth it out, then add the apples on top in an even layer. Add the rest of the cake batter on top of the apples and smooth it out with a spatula.
Bake the cake for 46-50 minutes, or until a toothpick comes out clean from the center.
Let the cake cool in the pan on a wire rack for 30 minutes, then pull up on the parchment paper to release it from the pan. Let the cake continue cooling on the wire rack until completely cooled.