• Preheat the oven to 300F degrees. 
• Line an 8x8 inch square baking pan with parchment paper or aluminium foil, leaving an overhang on each side. If using aluminum foil, lightly grease with butter or non-stick cooking spray.

Make the Base

• In a large bowl, beat the butter and sugar until combined.
• Turn the mixer down to low and beat in the flour, cornstarch and salt until combined. The mixture will be crumbly. 
• Press the mixture firmly into the bottom of the prepared pan. Bake for 20 minutes.
• Bake for 20 minutes. Remove from the oven and turn the oven to 350F degrees.

Strawberry Layer

• In a medium bowl, toss together the sliced strawberries, sugar, cornstarch, and orange zest until the straberries are evenly coated.

Crumb Topping

• In a medium bowl stir together the flour, brown sugar, white sugar, cinnamon and salt until evenly combined.
• Stir in the melted butter. The mixture should look like wet/damp sand.

Assemble and Bake

• Carefully spoon the strawberry mixture over the shortbread base until it's evenly covered. Any juice in the bottom of the bowl does not need to be spooned onto the shortbread base.
• Then crumble the topping over the strawberry layer. If you make a fist around the streusel and release your hand - it should form crumbles.
• Bake for 30-35 minutes until the streusel topping begins to turn golden brown and you can see the strawberry layer bubbling underneath.
• Remove from the oven and cool completely (about 4 hours or more) before slicing.
• To slice the bars, lift them out of the pan using the overhang of the parchment paper/aluminum foil. Place on a cutting board and slice using a shin, sharp knife (do not use a butter knife).