Bring the 300ml of water to a gentle simmer in a medium saucepan over medium heat. Remove from heat the moment simmering begins. Add the 15g of dried rose petals immediately and cover the saucepan. Steep covered for 10 minutes. The covered steep is the same technique from the elderflower tonic — rose petals' most volatile aromatic compounds (geraniol, citronellol, and various damascenone-family compounds responsible for the classic rose fragrance) evaporate readily as steam and the cover traps them within the steeping vessel, condensing them back into the liquid as the temperature declines. Uncovered rose petal steeping loses a significant proportion of the aromatic character; covered steeping retains it at the specific concentration that makes the finished drink taste unmistakably of rose without being perfumed. After 10 minutes, strain through a fine-mesh sieve and discard the rose petals. The finished rose infusion should be a pale golden-pink with a clearly detectable floral fragrance. Return the strained infusion to the clean saucepan.

Add the 250g of blackcurrants (fresh or frozen — frozen blackcurrants work equally well and often have an advantage of being available year-round at consistent quality), the 45g of honey, and the zest of 1 lemon to the rose infusion. Place over the absolute lowest available heat. Cook gently for 5 minutes, stirring occasionally, until the blackcurrants soften and visibly begin releasing their juice — the liquid deepening from the rose infusion's pale golden-pink to a deep, vivid purple-magenta as the blackcurrant juice extracts progressively into the surrounding liquid. The very low heat throughout is specifically important for two reasons. First, the rose infusion's delicate aromatic compounds — already extracted and distributed through the base water — are vulnerable to further evaporation at higher temperatures. The very low heat preserves them while still providing sufficient warmth to soften the blackcurrants and extract their colour and juice. Second, blackcurrant's most characteristic volatile aromatic compounds (particularly 4MMP, the same compound that makes Sauvignon Blanc wines specifically aromatic) are sensitive to prolonged high heat and diminish under aggressive simmering. Very gentle warming for 5 minutes extracts the berry's depth without cooking away the fresh, slightly wine-adjacent character that makes blackcurrant specifically more interesting than other dark berries.

Remove the saucepan from the heat. Allow to stand for 10 minutes. During this off-heat rest, the blackcurrants continue softening in the warm surrounding liquid and their colour and flavour continue extracting at a declining temperature. After 10 minutes, use a spoon or potato masher to mash the blackcurrants thoroughly into the liquid — pressing down and working the berry solids until they have broken down completely and the juice is fully extracted.

Strain the mixture through a fine-mesh sieve over a clean jug, pressing firmly on the blackcurrant and lemon zest solids to extract as much deep, vivid base as possible. Blackcurrant is a high-pectin fruit — the pressing will feel thicker and more resistant than the pressing of lower-pectin berries like raspberries. Press until the solids in the sieve are relatively dry. The finished strained base should be a deeply vivid, slightly thick, purple-magenta liquid with a concentrated aroma that combines floral rose, deep berry, and the lemon zest's bright citrus thread. Stir in the 30ml of fresh lemon juice. The lemon juice is added after straining rather than during the cooking for the same reason applied throughout this collection — its fresh, volatile aromatic character and clean acidity are preserved at room temperature and would be significantly diminished if added to the hot cooking liquid. Transfer to the refrigerator and chill completely — a minimum of 30 minutes.

Fill four large wine glasses generously with ice cubes. The large wine glass format is the specific choice for this preparation — the wide bowl both shows the vivid purple colour at its most visually striking and allows the dried rose petal garnish to be scattered over the ice surface with maximum visual impact. Divide the chilled blackcurrant rose base evenly among the glasses — approximately 80–85ml per glass, the relatively higher proportion of base to soda reflecting the blackcurrant's robust flavour concentration that needs the full serving to remain vivid through the soda dilution. Top each glass with approximately 125ml of chilled club soda, pouring gently down the inner side of the glass. Stir gently once or twice. Press a thin lemon slice against the inner side of each glass below the ice level. Scatter a small pinch of dried rose petals — food-grade, not decorative — directly over the ice surface of each glass. The petals provide both the visual signature of the drink and a delicate floral scent that rises with each sip's carbonation.