- Preheat your oven to 350°F (175°C). Grease and flour a 9×5 inch loaf pan.
- Make the streusel topping: In a small bowl, combine the flour, granulated sugar, brown sugar, and cinnamon. Cut in the cold butter using a pastry cutter or fork until the mixture resembles coarse crumbs. Set aside.
- Prepare the loaf batter: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
- In a large bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
- Gradually add the flour mixture to the butter mixture, alternating with the sour cream or Greek yogurt, beginning and ending with the flour mixture. Mix until just combined.
- Fold in the diced apples until evenly distributed throughout the batter.
- Assemble the loaf: Pour half of the batter into the prepared loaf pan. Sprinkle half of the streusel topping over the batter. Repeat with the remaining batter and streusel topping.
