Preheat the oven to 375 and grease your baking dish
Using a standing or hand-held mixer, cream together the butter and sugar. Add vanilla and egg and mix until fully combined
Hand stir in the milk until smooth
Mix or sift dry ingredients in a separate bowl and slowly add to the wet mixture, stirring until fully combined
Gentle fold in the blueberries and pour mixture into baking dish
In a separate bowl, use your hands to combine all of the Crumb Topping ingredients and then sprinkle on top of the buckle.
Bake in the oven for 45-50 minutes until cooked through and the top is golden brown.