Preheat and Prep: Preheat your oven to 350°F (175°C). Grease a 9-inch round or square baking pan.
Make the Streusel Topping: In a medium bowl, mix flour, brown sugar, cinnamon, and salt. Stir in melted butter until the mixture forms coarse crumbs. Add chopped pecans or walnuts and set aside.
Prepare the Cake Batter: In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg. In a large bowl, using a stand mixer (or hand mixer), cream the butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes. Add eggs one at a time, beating well after each addition, then mix in the vanilla extract. Add half the dry ingredients to the wet ingredients, mixing until just combined. Add sour cream and milk, mix, then add the remaining dry ingredients. Avoid overmixing to keep the cake tender. Gently fold in the grated apples (300g), which will add moisture and ensure the apples are fully cooked and integrated into the cake.
Assemble the Cake: Spread the batter evenly into the prepared pan. Sprinkle the streusel topping over the batter.
Bake: Bake for 50-55 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Let the cake cool in the pan.
Add the Glaze: Whisk powdered sugar, milk, and vanilla extract until smooth. Drizzle over the slightly cooled cake for a sweet, glossy finish.
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Notes
Apple Selection: Grating apples ensures they cook fully and distribute moisture evenly. Granny Smith adds tartness; Honeycrisp offers sweetness. Mix both (150g each) for a balanced sweet-tart flavor. Braeburn or Jonagold also work well.
Storage: Store in an airtight container at room temperature for up to 2 days or refrigerate for up to 5 days. Reheat slices briefly in the microwave for a fresh-baked texture.
Freezing: Wrap tightly in plastic wrap and foil, then freeze for up to 3 months. Thaw overnight in the fridge before serving.
Variation: Add a pinch of cardamom to the streusel for a unique twist.