Line an 8 x 8-inch square tin with parchment, and spray with nonstick spray. Preheat oven to 190° C / 350° F.

In a large mixing bowl or the bowl of a stand mixer, add butter, brown sugar, orange zest, and salt. Mix until fluffy and well combined.

In a separate bowl, whisk together the flour, oats, and baking powder.

Add the dry ingredients to the butter bowl. Use your hands to bring the mixture together, kneading gently until a crumbly dough forms.

Use your hands to press half of the crumble mixture to the prepared tin. Bake in preheated oven for 10 minutes, or until very lightly golden brown.

Meanwhile, stir together raspberries, sugar, orange juice, and cornstarch in a medium bowl.

Use a fork or plastic spoon to mash the raspberry mixture.

Spread over the partially baked crumble layer.

Drop remaining crumble mixture on top of the fruit layer, spreading it evenly over the surface of the pan. (It’s ok if the raspberries peek through in a few spots!) Return to oven and bake for 30 minutes, or until bubbly and golden brown. Transfer pan to a wire rack and allow to cool completely.

Grasping the edges of the parchment lining, the slab from the tin and transfer to a cutting board. Slice into squares and serve.

Store leftovers in an airtight container at room temperature for up to three days.