Preheat your oven to 180°C (350°F). Line an 8x8-inch square baking pan with parchment paper, letting a bit hang over the sides for easy removal later.
Make the crumble: In a mixing bowl, combine flour, granulated sugar, brown sugar, and melted butter. Stir with a fork or your hands until the mixture forms soft, clumpy crumbs.
Form the crust: Scoop two-thirds of the crumble into the prepared pan. Press it down gently but firmly to form an even crust.
Bake the crust for 12–15 minutes, or until lightly golden around the edges. Set it aside to cool for about 10 minutes while you prepare the filling.
Make the strawberry filling: In another bowl, mix together the sliced strawberries, strawberry jam (or sugar), and flour.
Once the crust has cooled a bit, spoon the strawberry filling evenly over the crust. It’s okay if it looks juicy!
Sprinkle the remaining one-third of the crumble on top. Don’t worry about covering the strawberries completely, the little pops of red peeking through will look pretty once baked.
Return the pan to the oven and bake for 30–35 minutes, or until the top is golden and the fruit is bubbling around the edges.
Let the bars cool completely in the pan so they firm up. If you’re in a bit of a hurry (or just excited to taste), you can cool them on the counter for 10 minutes, then pop the pan in the freezer for 15–20 minutes until set.
Make the glaze: In a small bowl, whisk together the icing sugar and milk until smooth and pourable.
Once the bars are completely cool, lift them out of the pan using the parchment overhang. Drizzle with glaze, then slice into 9 large or 16 smaller squares.