Preheat the oven to 350 degrees.  Butter a 12x9x2-inch pan.

Make the crumbs:

In a mixer, add melted butter and allow to cool for 5 minutes.  Add remaining ingredients and gently stir on low speed until the mixture becomes coarse and crumbly.  Do not over mix, as this will make the crumb mixture tough.  Set aside.

Make the batter:

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.   In a mixer, cream the butter and sugar until light and fluffy, approximately 6 to 8 minutes.  Add the eggs, one at a time, beating well after each.  Stir in the vanilla.  On low speed, alternately add the flour mixture and sour cream, beginning and ending with the dry ingredients.  Mix only until just combined.  Spread the batter in the prepared pan and smooth with a spatula.  The batter will be thick, so it needs to be nudged into the corners and evened out.  Grab a handful of the crumb mixture and gently squeeze it.  Break large clumps into smaller ones as you scatter over the batter.  There will be assorted size of crumbs, which is precisely what you want.  Make sure crumbs are spread out evenly, covering the batter.  Yes, you will have a lot of crumbs, but this is a chunky crumb cake after all.  Now, gently pat the crumbs into the batter.

Bake cake for 45 to 50 minutes, or until golden brown, and starting to pull away from the sides of the pan.  The cake may test done sooner than it is, so make sure the middle starts to dome.  Cover loosely with foil if the crumbs get too dark.  Make the glaze while the cake is cooking.

Make the glaze:

• In a bowl, combine powdered sugar, milk, and vanilla.  With an electric mixer on low speed, mix ingredients. 

Smother the warm cake with the glaze , cut into individual squares and enjoy!