At the Warehouse in Oxford, we had this prep guy who was from the outlaw boonies way out toward Tula; total stoner with a hot car and a girlfriend with a great rack and a space between her teeth. He used to sell homegrown in the parking lot.
He mopped the floor, proofed the bread, switched out the soda canisters, and made a whipped spread with buttermilk and margarine. I loved watching him do it. He’d crank up our big-ass Hobart with a perforated blade the size of a hubcap and start throwing one-pound blocks of margarine straight out of the cooler into the barrel-size bowl. The chunks made a whomp-bump racket until they began to soften. Then he’d start pouring in buttermilk, and the noise became a sliding hiss as the margarine and milk began to meld. The final product was a creamy, fluffy, flavorful spread the waiters served with warm loaves of bread on cute little wooden paddles.
We used margarine and low fat buttermilk for economy, but butter and whole milk buttermilk are worth the expense. Set your mixer on low speed; use the whip attachment. Begin adding softened butter one stick at a time. After the second stick is creamy, slowly begin adding buttermilk in a dribble. You should be able to incorporate about a little over a half cup of buttermilk to a pound of butter. As the mixture begins to meld, put your mixer on high and toss in about a teaspoon of salt. Whip until nice and fluffy. Refrigerate immediately.