Make the caramel sauce: Place the sugar and water in a small, heavy-bottomed saucepan over a medium heat. Do not stir. Watch as the sugar begins to melt around the edges, the crystals turning from white to a pale, transparent gold. Swirl the pan gently by the handle every now and then. The mixture will bubble and hiss, and the colour will deepen to a rich amber, like a sunset trapped in the pan. This takes about 6-8 minutes. The smell at this point is intoxicating—nutty, warm, and faintly smoky.

Finish the caramel: Once the sugar is a deep amber colour (think the colour of a conker), remove the pan from the heat. Carefully pour in the double cream—it will splutter and steam dramatically, so stand back. Whisk vigorously until the sauce is smooth and glossy. Stir in the vanilla, sea salt, and butter if using. The texture should be thick but pourable, like warm honey. Set aside to cool for 10 minutes. It will thicken further as it cools.

Prepare the coffee: While the caramel cools, brew your strong coffee. I use a stovetop moka pot, which gives a concentrated, slightly syrupy coffee with a rich crema. The sound of the coffee gurgling into the top chamber is one of my favourite kitchen sounds. Let the coffee cool slightly so it doesn't melt all your ice at once.

Assemble the glasses: Fill two tall glasses with ice cubes—generously, right to the top. The ice is your foundation, and you need enough so the drink stays bracingly cold without becoming watery too quickly. The clatter of ice against the glass is the first promise of refreshment.

Layer the flavours: Drizzle 2 tablespoons of the cooled caramel sauce around the inside of each glass. You want those sticky, golden streaks clinging to the glass. Pour the cold milk over the ice, filling each glass about two-thirds full. The milk will swirl and cloud as it hits the ice.

Add the coffee: Slowly pour the cooled, strong coffee over the milk. Watch the dark liquid cascade through the white milk, creating a beautiful marbled effect. The coffee will sink and mix, creating layers of flavour. Stir gently with a long spoon if you prefer a uniform colour, or leave it layered for a dramatic presentation.

Top and serve: For an extra touch of indulgence, whip a little double cream until it forms soft peaks, then spoon it on top of each drink. Drizzle with a final teaspoon of caramel sauce and a tiny pinch of sea salt. Serve immediately with a straw or a long spoon. The first sip should be cold, creamy, and deeply satisfying, with the caramel sweetness lingering on your tongue.