Preheat the oven and prepare loaf pan: Preheat the oven to 350°F. Grease a 9x5-inch loaf pan and line it with a single sling of parchment paper. Leave a 1-inch overhang of parchment paper on the long sides of the pan for easy removal after baking.

Make the streusel topping: In a medium bowl, combine the brown sugar, granulated sugar, flour, cinnamon, and salt. Slowly drizzle the melted butter over the dry ingredients, tossing the mixture with a fork as you pour. Once all the butter is added, mix until you have a crumbly, doughy mixture. Set aside.

Mix the dry ingredients: In a medium bowl, combine the flour, baking powder, baking soda, salt, and cinnamon. Set aside.

Combine the wet ingredients: Using a hand mixer or a stand mixer with a beater attachment, beat the butter and sugar on medium speed for about 2 minutes, until light and fluffy. Add the egg and vanilla extract and continue to mix on medium speed until fully combined. Add the yogurt and milk and mix on medium speed until all ingredients are evenly combined with a smooth, creamy texture.

Combine the wet and dry ingredients: Add the dry ingredients to the wet ingredients. Beat all the ingredients together starting on low speed and increasing to medium speed for 1-2 minutes, until a smooth batter forms with no lumps.

Fold apples into batter: Add the diced apples to the batter. Using a rubber spatula, fold the apples into the batter.

Pour batter into loaf pan: Pour the batter into the prepared loaf pan. Sprinkle the streusel over the top.

Bake: Place in the oven and bake for 45-50 minutes, until the streusel is golden-brown and a toothpick inserted in the center of the loaf comes out clean.

Cool: Let the apple bread cool in the pan for 10-15 minutes, then use the parchment overhang to lift it out of the pan and place on a wire rack. Let the loaf cool on the rack for an additional 5-10 minutes before slicing and serving.