Prep the Oven and Pan: Heat the oven to 350 F and grease and flour a 10-inch tube cake pan.
Streusel: Combine the brown sugar, flour, cinnamon, and a dash of salt in a medium bowl. Cut in the 3 tablespoons of butter to make a crumbly streusel mixture.
Dry Ingredients: Combine 2 1/2 cups of flour, baking powder, soda, and 1/2 teaspoon of salt in a medium bowl. Set aside.
Batter: In a mixing bowl with an electric mixer, beat the butter and sugar together for 3 minutes or until light and fluffy. Add the eggs, one at a time, beating well after each addition. Beat in the vanilla extract and sour cream. With the mixer on low speed, add the dry ingredients and beat just until combined.
Assembly: Spoon half of the batter into the prepared tube cake pan. Sprinkle about two-thirds of the streusel mixture over the batter, then top evenly with small dollops of the remaining batter. Gently spread the batter over the filling. Sprinkle the remaining streusel evenly over the top.
Bake: Bake the cake for 55 to 65 minutes or until a wooden skewer or toothpick comes out clean when inserted into the center of the cake.
Cool: Cool the cake on a rack for 30 minutes, then transfer the cake to a plate, streusel-side up. Carefully invert it onto a plate.
Glaze: Combine the glaze ingredients in a small bowl and drizzle over the cooled cake.