Heat the oven: Preheat to 350°F (175°C). Lightly butter a 9-inch square baking dish or similar 2-quart dish.

Prep the strawberries: Rinse, hull, and halve the berries. If they’re huge, quarter them. Pat dry with a paper towel so excess water doesn’t dilute the filling.

Make the filling: In a large bowl, combine strawberries, 1/2 cup granulated sugar, 1 1/2 tablespoons cornstarch, zest and juice of 1 lemon, and 1 1/2 teaspoons vanilla extract. Add a pinch of salt. Toss gently until the berries are evenly coated and glossy.

Transfer to the dish: Pour the strawberry mixture into your prepared baking dish, scraping in all the juices and sugar from the bowl.

Mix the crumble: In another bowl, stir together 1 cup all-purpose flour, 3/4 cup old-fashioned oats, 2/3 cup light brown sugar, 1/2 teaspoon salt, and 1/2 teaspoon ground cinnamon (optional). Add 1/2 cup (1 stick) cold unsalted butter, cut into cubes.

Form the crumbles: Using your fingertips or a pastry cutter, work the butter into the dry ingredients until the mixture forms clumps. You’re aiming for a mix of sandy bits and pea-sized crumbles. Don’t overwork it—small chunks melt into crisp, buttery pockets.

Top the berries: Scatter the crumble evenly over the strawberry filling. Leave a few small gaps so steam can escape and the topping crisps well.

Bake: Place the dish on a baking sheet to catch any drips. Bake for 35–45 minutes, until the topping is golden-brown and the strawberry juices are bubbling thickly around the edges.

Rest and serve: Let it cool for at least 15 minutes. The filling will set slightly as it rests. Serve warm with a scoop of vanilla ice cream for extra creaminess.

Make-ahead tip: You can mix the dry crumble ingredients and cut in the butter ahead of time. Store covered in the fridge for up to 2 days, then sprinkle over the fruit when ready to bake.