I have a ready-made homemade currant puree without sugar, you can just take 2-3 tablespoons of berries and mash them well.
We take a teapot, or, as I have, a French press, pour black tea there (green is possible, but it seems to me that black is more suitable), add clean currant leaves, mint, 5 rosemary needles (for the first time I do not advise any more) and a few currant berries.
And add berry puree or mashed berries, pour boiling water over everything and let it stand for 15 minutes.