Make the coffee cake: Preheat oven to 350F. Lightly grease an 8-in baking pan. Set aside.
In a large bowl, combine flour, baking powder, baking soda, and salt. In a separate bowl, beat butter and sugar until creamed. Beat in eggs, sour cream, and vanilla until smooth. Gently fold flour mixture into liquid until batter is just combined. Fold in chopped apples.
Scrape batter into prepared pan and smooth top. Set aside for a moment while you prepare the streusel.
Make the streusel: In a small bowl, toss streusel ingredients until crumbly and butter is evenly incorporated. Sprinkle streusel evenly over coffee cake batter.
Bake coffee cake at 350F 40-45 minutes or until a toothpick tests comes out clean when inserted in middle. Let coffee cake cool on a wire cooling rack 10 minutes, while you prepare the glaze.
Make the glaze: In a small bowl, whisk all glaze ingredients until smooth and drizzling-consistency. Drizzle glaze over warm coffee cake. Let cake stand 5 minutes, then slice into squares and serve warm.
Notes
Store coffee cake in an airtight container at room temperature up to 2 days.