Prepare the biscuit base: Preheat your oven to 180°C (160°C fan). Crush the digestive biscuits into fine crumbs—I put them in a sealed bag and bash them with a rolling pin until they feel like damp sand. Mix the crumbs with the melted butter and caster sugar until everything is evenly moistened. Press the mixture firmly into the base and up the sides of a 23cm loose-bottomed tart tin. Use the bottom of a glass to compact it—you want it tight so it doesn't crumble when sliced. Bake for 10 minutes until it smells toasty and the edges look slightly darker. Set aside to cool completely.

Make the lemon filling: In a medium saucepan, whisk together the egg yolks, condensed milk, lemon juice, and lemon zest. Place over a medium-low heat and stir constantly with a wooden spoon or silicone spatula. You’ll see the mixture start to thicken after about 5–6 minutes—it will go from a thin, runny liquid to a creamy, custard-like consistency that coats the back of the spoon. When it leaves a clear trail when you drag your finger across the spoon, it’s done. Remove from the heat immediately. Pour the filling into the cooled biscuit base and spread it evenly. Let it sit at room temperature for 15 minutes, then refrigerate for at least 2 hours until fully set.

Whip the meringue: In a large, spotlessly clean bowl, beat the egg whites with an electric mixer on medium speed until they become frothy and look like sea foam. Add the cream of tartar and continue beating. Gradually add the caster sugar, a tablespoon at a time, while the mixer runs. The mixture will transform from a bubbly liquid into a thick, glossy white cloud. Keep beating until it forms stiff peaks—when you lift the beaters, the meringue should stand up in firm points that don’t droop. Add the vanilla extract and beat for another 10 seconds. You’ll know it’s ready when it feels silky and holds its shape like shaving foam.

Assemble and toast: Spoon the meringue onto the chilled lemon filling, starting at the edges to seal them completely—this prevents weeping. Use a spatula to create dramatic peaks and swirls all over the top. For a professional look, I like to pull the meringue up into tall spikes. Now, you can either use a kitchen blowtorch (my preferred method) to toast the meringue until it's golden brown and smells like toasted marshmallows, or place the pie under a hot grill for 2–3 minutes. If using the grill, watch it like a hawk—it can go from golden to burnt in seconds. The meringue should develop dark caramel spots and a nutty aroma.

Cool and serve: Let the pie sit at room temperature for 20 minutes before slicing. This allows the meringue to settle and makes cutting cleaner. Use a sharp knife dipped in hot water and wiped dry between slices for the neatest presentation. Each slice should show the crisp biscuit layer, the sunny yellow curd, and the cloud-like meringue in perfect stripes.