Preheat the oven to 350 degrees F, grease a square cake dish - mine is 8**
Cut the butter into small pieces and combine it with the remaining ingredients in a small bowl, crumbling the mix together with your fingers. Refrigerate till ready to use
Stir together your flour, baking powder and salt in a small bowl. Set aside
Cream the brown sugar and butter together till creamy and fluffy - 3 to 4 minutes
Add eggs one by one, mixing 30 seconds between each addition
Now add in the vanilla, mix till combined
With the mixer on low alternately add the dry ingredients and milk, mix until combined. Be sure to scrape the bottom and side of your bowl.
Spread the batter into your prepared cake tin and then scatter the refrigerated crumb topping on top.
Bake for 30 minutes or until a skewer inserted in the middle comes out clean.