Place the almonds in a dry heavy-based saucepan over medium heat. Stir constantly for 3-4 minutes until the skins start to darken and the almonds smell nutty. Tip them onto a plate and set aside.

Line a rimmed baking sheet with parchment paper and brush it lightly with neutral oil or softened butter. Set a second sheet of oiled parchment and a rolling pin nearby - you'll need both quickly once the caramel is done.

Add the sugar, water, and lemon juice to the same heavy-based saucepan. Set over medium-low heat. Do not stir. Let the sugar dissolve and begin to bubble, swirling the pan gently once or twice if needed to even out the color.

Continue cooking, watching closely, until the caramel turns a deep amber - the color of dark tea or a copper coin. This takes about 10-14 minutes from when bubbling starts. If you have a thermometer, aim for 168-172 C / 335-340 F.

Remove the pan from the heat the moment the caramel reaches that deep amber. It continues cooking from residual heat, so don't wait for it to darken further in the pan.

Working quickly, add the toasted almonds to the caramel and stir with a silicone spatula until every almond is coated. The mixture will be thick and syrupy.

Pour the almond-caramel mixture onto the center of the prepared parchment sheet. Scatter a pinch of fine sea salt on top if using.

Lay the second sheet of oiled parchment on top and immediately use the rolling pin to press the brittle out to an even layer about 4-5 mm thick. Work fast - it begins to set within 60-90 seconds.

After 2-3 minutes, when the slab is partially set but still slightly pliable, use a sharp knife to score it into rough rectangles or diamond shapes. Press firmly but don't saw back and forth.

Leave the croccante to cool completely at room temperature for about 15 minutes until fully hard. Snap along the scored lines and transfer to an airtight tin lined with parchment.