|White wine||Dry x 9.0cl 3.0oz|
|Crème de cassis||1.0cl 0.33oz|
Crème de cassis is a fairly obscure liqueur in the states, but it makes up the key of this classic French aperitif.
French veterans may call for a larger ratio of crème de cassis as to emphasize the blackcurrant flavor a little more, but be careful not to overdo it (it's super sweet and will turn the cocktail cloying easily).
As for the cocktail's namesake and history, here's Wikipedia:
It used to be called blanc-cassis, but it is now named after Félix Kir (1876–1968), mayor of Dijon in Burgundy. Kir was a pioneer of the twinning movement in the aftermath of the Second World War, and popularized the drink by offering it at receptions to visiting delegations. Besides treating his international guests well, he was also promoting two economic products of the region. Kir allowed one of Dijon's producers of crème de cassis to use his name, then extended the right to their competitors as well. According to Rolland (2004), the reinvention of blanc-cassis (post 1945) was necessitated by the German Army's confiscation of all the local red Burgundy during the war. Faced with an excess of white wine, Kir renovated a drink that used to be made primarily with the red.