Instructions:
- Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan thoroughly.
- Make the Streusel: In a medium bowl, whisk together flour, brown sugar, cinnamon, and salt. Cut in the cold butter using your fingers or a pastry blender until the mixture resembles coarse crumbs. Place in the refrigerator to chill.
- Prepare Apples: Toss the sliced apples with lemon juice, granulated sugar, and cinnamon in a small bowl. Set aside.
- Combine Dry Ingredients (Cake): Whisk together the flour, baking powder, salt, and nutmeg in a separate bowl. Set aside.
- Cream Butter & Sugars: In a large mixing bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy (about 3–4 minutes).
- Add Eggs & Vanilla: Beat in the eggs one at a time, ensuring each is incorporated before adding the next. Mix in the vanilla extract. Scrape down the sides of the bowl.
- Alternate Wet & Dry: Gradually add the dry ingredients mixture to the wet ingredients, alternating with the milk. Begin and end with the dry ingredients (e.g., Dry, Milk, Dry, Milk, Dry). Mix only until just combined—do not overmix!
- Assemble the Layers: Spread half of the cake batter evenly into the prepared pan. Arrange the spiced apple slices evenly over the batter. Spoon the remaining batter over the apples. Sprinkle the chilled streusel topping evenly over the top layer.
- Bake for 50 to 60 minutes, or until a wooden skewer inserted into the centre comes out clean. If the streusel browns too quickly, loosely tent with foil for the last 15 minutes.
- Cool the cake in the pan on a wire rack for at least 15 minutes before slicing and serving warm or at room temperature.