Step 1: Prepare the Pan and Oven: Preheat oven to 350°F (175°C). Grease a 10-inch Bundt pan thoroughly and lightly dust with flour.
Step 2: Mix Dry Ingredients: In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, nutmeg, and allspice. Set aside.
Step 3: Cream Butter and Sugar: In a large bowl, beat softened butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Mix in vanilla extract.
Step 4: Combine Wet and Dry Ingredients: Alternate adding dry ingredients and apple cider to the butter mixture, beginning and ending with dry ingredients. Stir in sour cream and chopped apples (if using) until evenly incorporated.
Step 5: Bake the Cake: Pour batter into prepared Bundt pan and smooth the top. Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool in the pan for 10–15 minutes.
Step 6: Add Cinnamon Sugar Topping: Brush the slightly warm cake with melted butter. Mix sugar and cinnamon, then sprinkle evenly over the cake. Invert the cake onto a serving plate and allow it to cool completely.