Preheat the oven to 350 degrees Fahrenheit. Butter and flour a 10-inch bunt pan or tube pan. Set aside.

In the bowl of an electric mixer, add the butter and sugar. Cream for 4-5 minutes or until smooth and fluffy. Add the eggs one at a time, scraping the edges of the bowl in between. Add the vanilla and sour cream, and mix just until combined.

In a second large bowl, sift together the flour, baking powder, cornstarch, baking soda, and salt. With the mixer on low, slowly add the flour mixture to the butter mixture until just combined. Use a spatula to stir again, ensuring the ingredients are well combined and the flour is fully incorporated.

In a large bowl, add the brown sugar, flour, cinnamon, salt, and butter. Pinch together with fingers until the ingredients resemble a sand-like texture. Note: Be patient. This will take a while! Mix in the pecans, if using.

Spoon ½ the coffee cake batter into the prepared pan, spreading it out evenly with a knife. Sprinkle ½ the streusel mixture on top, making sure it does not reach the edges of the pan. Repeat with the remaining batter and streusel.

Bake for 45-50 minutes or until a cake tester can be inserted into the center and comes out clean.

Cool on a wire rack for 30 minutes. Carefully transfer the cake, streusel-side up onto a serving plate*

Create the glaze by whisking the powdered sugar, cream cheese, and milk until smooth. Add a few drops of water as needed to thin it out. Drizzle the glaze evenly over the cake.