Blackcurrants? Amazing. Read about how to grow them here. But then what?
To make your own cassis, take a pound of black currants, wash well, and seal in a jar with one 750 ml bottle of grappa, grape eau-de-vie, marc, or good vodka. (I’d choose Ciroc, a vodka distilled from grapes.) Mash the fruit to release the juice, and let it sit for a month, shaking or stirring the jar once a week. Then strain into a new container and add simple syrup (equal parts sugar and water, heated and allowed to cool) to taste. One to two cups simple syrup should do it. Give it a couple more months, and it should be ready to drink.
A Kir, by the way, is simply a splash of cassis topped with dry white wine. Add sparkling wine instead and it’s a Kir Royale. Add cider and it’s a Kir Cidre. You get the idea.
To see a Kir in action, check this out–