• Preheat the oven to 350°F. Spray an 8x8 pan with cooking spray and line with parchment paper. Set aside.

Make the crumb topping.

• In a small, microwave safe bowl, melt the butter. Set aside.
  6 Tablespoons unsalted butter
• In a medium bowl, whisk together flour, both sugars, spices, and salt.
  1 ⅛ cups all-purpose flour, ¼ cup dark brown sugar, 2 Tablespoons granulated sugar, 1 ½ teaspoons ground cinnamon, ¼ teaspoon ground nutmeg, 1 pinch fine sea salt, ⅛ teaspoon ground cloves
• Add melted butter to the flour mixture and toss with a fork until fully moistened. Cover the crumbs and place the bowl in the fridge while you make the cake batter.

Make the cake batter.

• In a large bowl, whisk to combine flour, sugar, baking powder, baking soda, and salt.
  1 ¼ cup all-purpose flour, ¾ cup granulated sugar, ¾ teaspoon baking powder, ¼ teaspoon baking soda, 1 pinch fine sea salt
• Cut the butter into squares and add it to the bowl with the flour mixture. Using a pastry cutter, cut the butter into the flour mixture until it's the texture of coarse meal.
  ¼ cup unsalted butter
• In the same bowl you used to melt the butter for the crumb topping, whisk together the egg, sour cream, milk, and vanilla until well blended.
  1 large egg, ½ cup full-fat sour cream, 2 Tablespoons whole milk, 1 teaspoon vanilla extract
• Add the wet ingredients to the bowl with the flour and stir just until blended.
• Add ½ cup (53 grams) of the chopped apple to the bowl and fold it into the batter.
  ½ cup chopped apple

Assemble and bake the coffee cake.

• Add half of the cake batter to the prepared pan. Use a rubber or offset spatula to spread the batter to the edges of the pan.
• Spread half of the crumb mixture over the batter in the pan, using your fingers to crumble it into small crumbs and ensuring the batter is evenly covered and the crumbs reach to the edges.
• Sprinkle ¼ cup (27 grams) of the chopped apple over the crumb filling.
  ¼ cup chopped apple
• Add the remaining cake batter on top of the filling, using the spatula to gently and carefully spread the batter over the crumbs so that the crumbs are completely covered and the batter reaches to the edges of the pan. (Adding dollops of batter evenly over the top makes spreading the batter over the crumbs much easier. A small cookie scoop is useful here.)
• Sprinkle the remaining ½ cup (53 grams) of chopped apple over the batter.
  ½ cup chopped apple
• Spread the remaining crumb mixture over the top of the batter and apples, again using your fingers to crumble it into small crumbs and ensuring the batter is evenly covered and the crumbs reach to the edges.
• Bake the cake for about 45 minutes or until the cake is puffed and golden brown and the top springs back when gently poked. Let the cake cool in the pan on a wire rack for at least 30 minutes.

Make the glaze.

• In a small bowl, whisk together the confectioners' sugar and milk. The mixture should be thick but pourable. Spoon the glaze over the cake.
  ¼ cup confectioners' sugar, 1 ¼ teaspoons whole milk
• Remove the cake from the pan, slice, and serve. Be sure the cake is completely cool before storing.