If you are reading this over breakfast and want to be a part of the latest diet fad, then take a tablespoon, lift the butter dish and stir two great dollops of the yellow stuff into your coffee.
Add a dash of oil and, hey presto, you have a steaming cup of Bulletproof Coffee, otherwise known as "the fat black".
The heady brew, caramel-brown with an unhealthy oily sheen, if done correctly, contains up to a whopping 500 calories a cup. This is the new weight-loss craze sweeping the US and now creeping into the UK.
The coffee, the lardy contents of which have left nutritionists dismayed, has been developed by tech millionaire Dave Asprey. The 41-year-old discovered the "power of butter" thousands of metres above sea level while hiking near Mount Kailash, in Tibet.
"I staggered into a guest house from the minus-10C weather and was rejuvenated by a creamy cup of yak butter tea," so Asprey's story goes.
But such concoctions, say its many critics, encourage the worst in modern-day narcissism and will no more help you lose weight than a bacon sandwich.
"There is no science that would back this up as a weight-loss tool," said Sally Norton, a UK surgeon and weight-loss consultant.