Crumble Base

1. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugars until light and fluffy, about 3 minutes. Scrape down the sides of the bowl.
2. Add the egg and vanilla, mixing to combine well. Scrape down the sides of the bowl.
3. In a separate bowl, whisk together the flour, baking powder and salt.
4. Add the dry ingredients and mix just until the dough starts to pull away from the sides of the bowl. Do not over mix.
5. Set aside roughly 2 cups of the dough (loosely packed) and cover to reserve to use on the top of the crumble.
6. Press the shortbread dough into the an 8 x 8 baking pan lined with parchment paper. Use your hands or the flat side of a measuring cup to press it evenly into the corners of the pan.
7. Bake at 350°F for 13 to 15 minutes, or until the edges are slightly golden brown and the center is just set. Do not over bake.
8. Remove the pan from the oven and allow the crust to cool slightly while you make the strawberry filling.

Strawberry Filling

1. Wash, de-stem and quarter the strawberries. If using frozen strawberries, add them straight to the pot. 
2. Add the sugar, water (omit if using frozen berries) and cornstarch. Stir to combine.
3. Bring the mixture to a simmer over medium-low heat and continue to stir frequently. Use a fork to mash the berries in the pot, helping to break down the fruit and release the juices. The mixture will begin to thicken as it cooks.
4. Continue to simmer the mixture for about 6 to 8 minutes until thickened. Test for doneness using the spoon test. Dip the back of a spoon into the mixture and then draw a line through it with your finger. The “jam” should stay separated on the spoon. If the line fills back in with the jam, continue cooking for 1 to 2 minutes and test again. Remove the filling from the heat and transfer to a medium bowl to cool slightly.

Crumble Topping

1. Once the crumble base and strawberry filling have cooled slightly, pour the filling over the base and use a spatula to spread it evenly across the top. 
2. Use your hands to make small round discs with the reserved dough, placing them randomly over the top of the filling. For best results, allow bits of the strawberry filling to peak through.
3. Bake for 40 to 45 minutes or until the top is golden brown and the strawberry filling is bubbling below. Remove the bars from the oven and cool completely on a wire rack before drizzling with the glaze.

Glaze

1. Add the powdered sugar, milk and vanilla (optional) to a medium bowl. Whisk together until smooth and pourable. If the glaze is too thick, add more milk. If too thin, add more powdered sugar.
2. Drizzle the glaze over the top of the cooled bars.