Using an electric mixer in a large bowl, cream together butter and cream cheese. Beat in sugars until light and fluffy. Add the egg, beating until combined. Scrape down the sides and bottom of the mixing bowl with a rubber spatula. Stir in vanilla extract.

In a separate, medium-sized bowl, whisk together flour, baking powder, cornstarch, and salt. Gradually add flour mixture to wet ingredients, alternating with buttermilk, until all of the flour mixture and buttermilk have been combined.

Spread about half of the batter into the prepared pan (the batter will be thick).

Make the cinnamon swirl: Whisk together sugar and cinnamon for a cinnamon ripple layer in a small bowl and sprinkle it evenly over the batter.

Dollop the remaining batter over the cinnamon sugar layer and use a spatula to spread evenly over the top. (If it gives you a tough time/doesn't want to spread, just try your best but dont stress. If it's easier, just swirl the cinnamon/sugar in with a knife. Set aside and prepare your streusel topping).

Make the streusel: Melt the butter in a medium-sized bowl in the microwave in 10-second increments (stirring between) until just melted (you don't want it to be too hot. If it does get too hot, allow it to cool).

Use a fork to stir together the flour, sugars, cinnamon, and salt. Pour melted butter over the mixture and use a fork to toss/claw together the ingredients until combined (mixture should be crumbly).

Sprinkle streusel evenly over the batter.

Bake in the oven for 40-50 minutes (check doneness with a toothpick inserted in the center; it should come out clean or with a few moist crumbs).

Make the glaze: While the cake is cooling, whisk together powdered sugar and milk. Drizzle over cooled coffee cake.

Brew and prepare the coffee to your liking.