To make the crumble, preheat the oven to 375 degrees F/190 degrees C. Butter or spray with cooking spray 7 x 7-inch/18 x 18-cm square cake pan. Line it with parchment paper, hanging it over two sides. In a medium mixing bowl, place oatmeal, flour, brown sugar, and mix. Add cold butter and mix until the mixture gets crumbly and sticks under the pressure of fingers. Press two-thirds of the mixture into the bottom of the pan.

To make strawberry filling, in a separate bowl, mix fresh strawberries cut into four lengthwise, granulated white sugar and cornflour.

Spread strawberry preserves over the crumb crust, then distribute the fresh strawberry filling. Using your hands, cover with the remaining crumble. Bake for about 50 minutes or until the top is golden brown. Remove from the oven and let cool for 10 to 20 minutes in the pan. Lift the crumble out of the mold using parchment paper. Let cool completely. Cut into squares.