Preheat the oven to 350'F. Grease the 9 x 9 inch pan and put a piece of parchment paper in the bottom and sides of the pan. This will help you remove it easily.

In a medium sized bowl, make the topping. Add the cold butter, sugar and flour. Mix together until it forms a crumble. Set aside.

In a bowl, add the egg, butter, flour, cornstarch, baking powder and sugar. Mix together with your hands until a dough forms that holds together.

Transfer the dough to the 9x9 inch pan, and spread it out evenly to the bottom and sides of the pan. It might take a minute or two to get it spread out and it will be somewhat thin, but make sure the entire bottom and sides of the pan are covered.

Using a fork, prick the shortbread dough that you just put into the pan. This helps to reduce the crust from puffing up or making bubbles.

Bake the crust in the preheated oven for 15 minutes or until golden brown. Allow it to cool as you make the fruit layer.

In a medium sized bowl, add the chopped strawberries and rhubarb. Add in the cornstarch and sugar, then stir together until combined.

Once the crust is done baking, pour the fruit mixture on top of the crust. Add the streusel topping and press it down into the fruit mixture. Put it back into the oven to cook for another 50-60 minutes.

Crust and topping should be a light golden brown when ready. Slice into 9 pieces and enjoy!