This is a loose-leaf herbal tea, which means the leaves need room to open and release their flavour. A typical starting point is to use about 1 teaspoon (roughly 1–2 grams) of dried leaves per 200–250 ml of water. Place the leaves directly in a cup or a teapot with a strainer.
Water temperature matters: black currant leaves are delicate, so boiling water can make the infusion overly bitter or harsh. Let the water cool for a minute after boiling, to about 90–95°C. Pour it over the leaves and steep for 3 to 7 minutes. A shorter steep gives a lighter, more delicate cup; a longer steep brings out more of the tangy, slightly astringent character. Taste after 3 minutes and decide if you want it stronger.
Because the leaves are whole and loose, they need time to unfurl. Stir gently once after pouring the water to help them soak. You can also re-steep the same leaves once, though the second cup will be milder. If you prefer a very mild infusion, use less leaf or a shorter steep. There is no fixed rule — adjust the amount and time to suit your palate.