Position rack in center of oven. Preheat oven to 325°F/165°C. Coat a 12-cup/2.9 L tube pan generously with nonstick spray.

For the Streusel: Melt the butter in a medium sized mixing bowl in microwave. Whisk in brown sugar, cinnamon and salt, then stir in the flour. Create crumbs by squeezing together with fingers. (You can melt butter on stovetop too, if you like, then transfer to a mixing bowl). Set aside.

For the Cake: Whisk together the flour, baking powder, baking soda and salt in a medium bowl to aerate and combine; set aside.

Beat the butter until creamy with the flat paddle attachment of a stand mixer on medium-high speed until creamy, about 2 minutes. Add sugar gradually and continue to beat for, about 3 minutes at medium-high speed, until very light and fluffy. Beat in vanilla. Add the eggs one at a time, beating well after each addition, scraping down the bowl as needed. The mixture might look curdled; that’s okay. Add the flour mixture in three additions, alternately with the sour cream. Begin and end with the flour mixture and beat briefly until smooth.

Scrape a little over half of the thick batter (you can do this by eye) into the prepared pan and smooth the top with a small offset spatula. Sprinkle a scant half of the streusel evenly over the batter covering it completely. Top with remaining batter, spreading carefully with an offset spatula to cover the streusel, then top with remaining streusel, covering entire surface. Press gently into the cake batter.

Bake for about 55 to 65 minutes or until a bamboo skewer shows a few moist crumbs. The streusel will be golden brown and the cake will crown a bit. Cool in the pan on a rack for at least 20 minutes; the pan should be barely warm. Unmold, re-invert and place right side up on rack. Once cooled transfer to a display platter.

For the Optional Glaze: Place confectioners’ sugar in a saucepan. Whisk in water until beginning to combine; it will be very thick before you heat it. Cook over medium heat, whisking often, until it liquefies, becomes completely smooth and very warm to the touch. Do not let it get too hot or simmer. This cooking will be brief - about 15 seconds, give or take. Whisk until completely smooth and use immediately.

Drizzle glaze over cake using a spoon or fork. It will set almost instantly. The cake is ready to serve. Store at room temperature in an airtight container for up to 3 days.