Preheat oven to 350°F. Spray a tube pan with baking spray or butter and flour. Set aside.
In a large bowl using a whisk, sift together flour, baking powder, baking soda and salt. Once combined, add sugar. Whisk until combined.
In a separate bowl whisk together buttermilk, butter, vanilla and eggs.
Add wet to dry ingredients. Mix by hand until fully moistened and lumps are dissolved. Pour half of batter into tube pan.
To make the streusel: In a medium size bowl, mix together brown sugar, flour and cinnamon. Cut in butter using a pastry blender or rub with your hands until it resembles peas. Add 1 cup chopped pecans or walnuts. Mix well.
Sprinkle 1/2 streusel over batter.Top with remaining cake batter ending with streusel.
Bake for 55-60 minutes. or until a toothpick inserted into the cake portions shows moist crumbs. Check at 30 minutes and lay foil on top to prevent over browning, if needed.
Cool in the pan on a baking rack for 30 minutes. Remove from the pan and cool completely.
Mix together glaze and drizzle on top once cooled. Store in an airtight container at room temperature or chilled.