Preheat the oven to 350 degrees. Butter and flour your bundt pan and set aside.

Whisk together the sugar, flour, cinnamon, cocoa and salt. Add the butter pieces and using your hands, mix together the flour and butter until the flour is incorporated and in tiny pieces.

In a small bowl, whisk together the flour, baking powder, soda and salt, set aside. In the bowl of your electric mixer, beat the butter and sugar on medium speed until until fluffy, about 4 to 5 minutes, scraping down the sides as needed. Add the eggs one at a time, beating well for 1minute after each egg. Add the vanilla and sour cream, and mix well.

Add the dry ingredients to the wet ingredients with the mixer on low speed, just until incorporated. Spoon half of the batter into the prepared pan, then sprinkle with 2/3 of the streusel. Spoon in the remaining batter on top and smooth. Sprinkle the remaining streusel on top. Using a butter knife, loosely swirl the streusel into the batter, making sure you don’t overswirl (just about 10-12 swirls will do).

Bake until a toothpick or cake tester inserted into the cake comes out with just a few moist crumbs, about 45 to 55 minutes. Remove the cake from the oven and allow to cool for 10 minutes. Invert the pan on a wire rack and allow the cake to cool completely. Spread the glaze onto the cooled cake and serve.

While the cake is baking, make the glaze by adding the butter to a small saucepan and cook over medium heat. Swirl the pan frequently (whisking works too) until the butter begins to bubble and turn golden brown (brown bits start to appear on the bottom of the pan), remove it immediately from the heat. (This will take about 5 minutes and it will all of a sudden turn golden brown, so watch it closely). Pour the browned butter to a bowl and whisk in the sugar, vanilla extract and milk (use as much as needed to get desired consistency).