How to butter-roast coffee in frying pan?

I have been roasting coffee for a few years and have never heard of this. It wasn't so easy to find on Google. From An Overview of Vietnamese Coffee:

Thirdly, beans are generally roasted in what is referred to as "butter oil", which may or may not be actual clarified butter oil. Occasionally vegetable oils are used, and historically, traditional "home-grown" coffee roasting style involves creating almost a caramel-like coating effect with the use of a small amount of sugar, oil, and generally a touch of vanilla or cocoa. This coating blackens in the roast and the beans wind up with almost a thin, hard shell. Why is this done? Robusta beans are uniquely slow to ripen on the bush, and often pickers pick unripe beans along with ripe beans. The traditional coating gives all the beans a similar color. The presence of a few unripe beans does not hurt the overall taste effect of the blend. However, modern growers pick only ripe beans despite the extra labor, and do not feature this coating in their roasting, opting simple for a little oil to keep the beans easy to turn in the slow roasting process.

I also googled pan roasting techniques. Apparently you should be able to achieve a roasting time of 15-20 minutes. So you are spending several minutes at 200C. With such a small amount of butter and sugar, I wonder when you add the extra ingredients to the pan so as to not burn the coating.

If just using the oil to help the beans turn, then I imagine adding the oil from the start will work.

I might have to try this myself.

Just frying them in butter won't work. The temperature needed to roast the bean is much higher than the milk solids can handle. If I were you, I'd begin by clarifying the butter to get rid of the milk solids, then use the clarified butter with the same method you are using now.

References:

• Temperature scales for various roasts at the bottom
• One way to make clarified butter

I've added about one tablespoon of butter on the beans while turning them constantly in the frying pan at about a crack and a half.... When finished it leaves a high gloss on a medium roast. The flavor is wonderful and it seems to make for an even smoother more rich flavor.

You can roast in a pan in the oven, stirring every few minutes, or in the same upon the top of the range. Stir often, and roast quickly to a bright brown, not a dull black. While still hot, beat up the white of an egg with a tablespoonful of melted butter, and stir up well with it. This will tend to preserve the flavor.