Add the sugar, water, and salt to a small saucepan. Warm over medium heat, stirring until the sugar fully dissolves. Remove from the heat and stir in the vanilla extract. Cool completely before using. The syrup should be smooth and pourable, not thick or sticky. Thick syrup does not mix cleanly into cold coffee or cold foam. Letting the syrup cool fully before it's used in either the cold brew base or the chocolate cream matters directly — warm syrup added to cold liquid would begin warming it unevenly, working against the temperature control both later stages depend on.

In a small jug, whisk the cocoa powder with the vanilla syrup and salt first, forming a smooth chocolate paste. Add the heavy cream and whole milk, then whisk until fully combined. The cocoa needs to be fully dissolved before frothing. If you dump dry cocoa straight into cold cream, it floats, clumps, and gives you ugly specks in the foam. Use cold cream and cold milk. Warm dairy foams poorly and collapses faster. Building this paste first, using the syrup's liquid to fully wet and dissolve the dry cocoa before any dairy is introduced, is exactly what prevents the powder from floating and clumping — cocoa's fine, somewhat hydrophobic particles need that concentrated liquid contact to properly disperse before being diluted further into the cream and milk.

Froth the chocolate cream with a handheld frother, milk frother, French press, or drink mixer until thick, smooth, and softly aerated. It should be spoonable and dense, but still loose enough to slowly sink into the cold brew. The foam should look like soft chocolate cream, not whipped cream. If it becomes stiff and mound-like, it is over-frothed. If it pours like plain milk, it is under-frothed. This specific target texture, sitting deliberately between two failure states, is worth checking for by feel and appearance rather than a fixed frothing time — different frothers and different cream temperatures can reach that ideal point at slightly different speeds.

Add 10ml vanilla syrup to each glass. Fill each glass generously with ice, then pour in 180ml cold brew coffee per glass. Stir briefly to combine the vanilla syrup with the cold brew. The base should stay dark and strong. Chocolate cream is rich, so weak cold brew gets buried immediately. Given how rich and assertive the chocolate cream foam is, this coffee base needs genuine strength specifically to remain noticeable once the two components are eventually combined and stirred together.

Spoon or slowly pour the chocolate cold foam over each glass, dividing it evenly. Let the foam sit clearly on top of the dark cold brew. The finished drink should show a strong contrast: dark coffee underneath and a thick pale chocolate-brown foam layer above. If the foam disappears instantly, it was too thin or the coffee base was too warm. Both possible causes named here point to the same underlying requirement — proper foam density from correct frothing, and a properly cold coffee base — either failing on its own is enough to collapse the drink's defining visual contrast.

Serve immediately without stirring first. The drink should be presented with the chocolate foam sitting on top, then stirred before drinking if desired. The foam naturally softens and begins blending into the coffee the moment it's poured, so presenting and serving the drink without delay is what preserves that sharp, layered contrast at its most striking.