Preheat your oven to 180°C (350°F). While it heats, grab a 20cm square baking dish or a similar-sized ovenproof skillet — no need to grease it if you're using a non-stick surface.

Prepare the berry filling directly in the dish: Tip the frozen berries straight into your baking dish. Sprinkle over the 60g powdered sweetener, lemon juice, vanilla, and arrowroot powder. Stir gently with a fork until the berries look glossy and the powder has mostly disappeared. You'll see a few icy crystals still clinging to the fruit — that's fine; they'll melt during baking.

Make the almond crust topping in the same bowl: In a separate medium bowl (or if you're being clever, use the bowl you just used for the berries after a quick wipe), combine the almond flour, chopped nuts, remaining 60g sweetener, cinnamon, and salt. Pour in the melted butter and stir with a fork until the mixture resembles damp, crumbly sand. It should clump together slightly when pressed between your fingers — that's the sign you're after.

Assemble the crisp: Sprinkle the topping evenly over the berries. Don't press it down — leave it loose so it can form those golden, crunchy clusters as it bakes. The berries should still be visible peeking through the topping in places.

Bake until bubbling and golden: Place the dish on a baking tray to catch any drips (trust me on this). Bake for 22–28 minutes. You'll know it's ready when the berry juice is bubbling thickly around the edges — you'll hear it hissing and popping — and the topping has turned a deep, toasted brown. The kitchen will smell like a bakery.

Rest before serving: Pull the dish out and let it sit for at least 10 minutes. This is crucial — the filling needs time to set into a jammy, spoonable consistency rather than a runny mess. The topping will also firm up slightly as it cools, giving you that satisfying crunch.