The topping is somewhere between a crumb topping and a sugar cookie dough, which means it bakes up into these golden, slightly crispy, slightly chewy clusters that are absolutely irresistible. You'll find out what that secret ingredient is when you get to the recipe — trust me, don't skip it. Serve it warm with vanilla ice cream or custard and you will not have leftovers.

Preheat your oven to 350°F with a rack in the centre. Lightly grease your baking pan — I use a 10×15 glass Pyrex for a big batch. You can put a cookie sheet underneath the Pyrex pan to catch any of the fruit juices that might bubble over.

In a large bowl, gently stir together all the filling ingredients. Transfer to the prepared pan.

In a medium bowl, combine the sugar, flour, baking powder, and salt. Add the vanilla extract and melted butter and stir until fully combined. The mixture will look like a cross between a crumb topping and a sugar cookie dough — that's exactly right.

Press pieces of the topping together with your fingers to form different irregular-shaped pieces of crumble topping. Scatter it all over the top of the fruit filling.

Bake for 30–35 minutes, until the fruit is bubbling and the topping is beginning to turn light golden brown. Transfer to a wire rack and cool for about 15 minutes — the juices will thicken up as it sits.

Serve warm with a scoop of vanilla ice cream or a pour of vanilla custard.

Freeze the blackberries first.Pop them in the freezer before you start, so they hold their shape when you mix the filling instead of turning to mush.

Any berries work here.If you don't have blackberries, use whatever you have — strawberries, cherries, raspberries, blueberries, or a mix. Halve or quarter the strawberries. If your berries are very juicy, add a few extra tablespoons of flour to the filling to help it set up.

Adjust the sugar.Taste your fruit first. If your apples are already quite sweet, start with ¼ cup sugar. If they're tart, go up to ½ cup.