In a medium sized mixing bowl, combine the chopped apples (from 2 baking apples, peeled and chopped), ¼ teaspoon ground cinnamon and 2 Tablespoons granulated sugar. Stir until apples are coated; set aside.
In a medium sized mixing bowl, sift or whisk the 1/2 cup all-purpose flour, 1 ¾ teaspoon baking powder, ¼ teaspoon salt, and ½ teaspoon ground cinnamon.
In the bowl of a stand mixer or a large mixing bowl, cream together the 1 ½ cups unsalted butter, and 2 cups granulated sugar until light and fluffy, around 3 minutes. Add in the 4 large eggs, one at a time, followed by the 1 ½ teaspoons vanilla extract.
Alternate adding in the sifted dry ingredients with the ½ cup sour cream,, beginning and ending with the dry ingredients. Pour 2/3 of the batter into a greased Bundt or tube pan.
In a small mixing bowl, cut the slightly 4 Tablespoons unsalted butter, into the 1/2 cup all-purpose flour and 1/3 cup brown sugar,
Sprinkle the chopped apple mixture over the batter, followed by 2/3 of the streusel mixture. Spread remaining cake batter on top of the apple and streusel mixture, then sprinkle the remaining streusel mixture on top of the cake.
Bake at 350°F for around 1 hour, or until a toothpick inserted in the middle comes out clean.
Allow cake to cool in pan around 15 minutes; run knife around edge and gently invert into a wire rack. Once cake has cooled, combine the glaze ingredients (2 cups powdered sugar, 2 Tablespoons water) and drizzle over cake. Serve once glaze has set.