I love cultured butter! Cultured butter starts with cultured cream. The "culturing" results from leaving cream at left at room temperature to spontaneously sour as its own beneficial bacteria proliferate OR it results from the cream being innoculated with
Cultured Dairy: How to Make 1 Stick of Butter, 1 Pint of Sour Cream, and 1 Pint of Buttermilk with JUST ONE Quart of Cream
NYT Cooking: Cultured Butter Cookies These cookies are crumblier, crisper and more buttery in flavor than the typical cookie made with high-fat sweet cream butter. Which is exactly why you should make them.