We only use butter, no margarine, but Irish butter is too expensive for me. I tried to make butter a while back, souring the cream with a little yogurt overnight, etc. But I used pasteurized cream, and it just doesn’t work the same. It had almost no flavor, and makes so little, it’s just cheaper to buy butter on sale.
Don’t use yogurt, us a buttermilk with live cultures. Gotta let it set for a bit to thicken. Then whip it. Pasteurization is OK, ultra pasteurized is not, because ultra pasteurization changes proteins in the milk/cream. Butter will form even without culturing it.