Sift together the dry ingredients and the spices into a small bowl.
Add the white sugar. Whisk into the dry ingredients.
In a large bowl, whisk eggs until light and fluffy, about 2 minutes.
Add the buttermilk, melted butter, and vanilla to the eggs and whisk until combined.
Chop apples into 1-inch cubes. Toss apples and pecans into the dry ingredients.
Fold together until combined.
The batter will be very thick - this is normal!
Grease two loaf pans (see note) and coat them in a light layer of flour.
Divide the batter evenly between the loaf pans.
Combine the brown sugar and oats.
Sprinkle over the top of the loaf pans. Dot with the cold butter.
Bake for 50-55 minutes, or until a toothpick comes out clean.
Let cool in the pans for 20 minutes and then turn out onto a cooling rack to cool completely.
Notes
Use any kind of apples you like, I like to use a sweeter apple rather than a tart one. My favorites are gala and honeycrisp. You can use standard size loaf pans, either 9x4 inches or 10x5 inches.