Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan and line it with parchment paper, leaving some overhang on the sides for easy removal.

For the streusel topping, combine ½ cup all-purpose flour, ⅓ cup packed brown sugar, and 1 teaspoon ground cinnamon in a small bowl. Cut in 3 tablespoons cold, cubed unsalted butter using a fork, pastry cutter, or your fingers until the mixture resembles coarse crumbs with pea-sized bits of butter still visible. Set aside.

In a medium bowl, whisk together the dry ingredients for the bread: 2 cups all-purpose flour, 1½ teaspoons baking powder, ½ teaspoon baking soda, ½ teaspoon salt, 1 teaspoon ground cinnamon, and ½ teaspoon ground nutmeg.

In a larger bowl, cream the ½ cup softened unsalted butter with 1 cup granulated sugar until light and fluffy, about 2-3 minutes. Then beat in 2 large eggs one at a time, followed by 1 teaspoon vanilla extract and ½ cup sour cream (or plain Greek yogurt).

Gently fold the dry ingredients into the wet mixture until just combined—be careful not to overmix. Fold in 1½ cups of peeled and diced apples.

Pour the batter into the prepared loaf pan. Evenly sprinkle the prepared streusel topping over the batter and bake for 55-60 minutes until a toothpick inserted in the center comes out clean.

If using the optional glaze, whisk together ½ cup powdered sugar, 1-2 tablespoons milk or cream, and ¼ teaspoon vanilla extract. Drizzle the glaze over the cooled bread before serving.