Combine the melted butter, flour, sugars, cinnamon, in a bowl butter in a small bowl. Set aside in the fridge to chill while you prepare the batter.

Preheat oven to 350 F. In a small pot, bring the apple cider to a boil over medium high heat. Reduce heat to medium and simmer until cider is reduced down to 1/2 cup. Set aside to cool before using. Butter and line an 8 inch pan with parchment paper leaving a two inch overhang on the sides. In a medium sized bowl, sift together the flour, baking powder, baking soda, salt and spices.

In a large bowl or the bowl of an electric mixer, beat the butter and sugars, on medium speed until light and fluffy. Scrape down the sides of the bowl and add the vanilla followed by the egg. Add the apple cider followed by the sour cream. Stir in the flour until just combined and stir in the apples. 

Spoon the batter into pan. Use a spatula or an offset spatula to spread the mixture evenly in the pan. Tap sharply to reduce air bubbles. Sprinkle 1/2 cup chilled streusel over the cake batter. Sprinkle the streusel evenly over the top of the batter. Bake 25-32 minutes or until a toothpick comes out clean when inserted in the center.  Cool in pan on a wire rack for at least 1 hour before adding the glaze and serving.

Whisk the powdered sugar, apple cider and pinch of salt together in a small bowl. Drizzle over the cooled cake.