A documentary about the American dream – but which, through a variety of episodes and moods, shows us that despite the dream and the wonders of fulfilment, there is the ever-present danger of the dream turning to nightmare.

Film reviewers sometimes have to offer a caution, that they are personally involved in the narrative, or in the issues. In this case, the present reviewer has to confess to never having liked donuts. And, to say the least, here are 90 minutes of hundreds and hundreds of donuts, of all varieties – and more. So, these words from the rather detached point of view, at least from the perspective towards the donuts themselves.

We are in no doubt from the first 10 minutes of this documentary about the place of donuts in the American menu – sugar, icing and sweetness – and in the American psyche. Dunkin’ Donuts, Winchells, all kinds of donut shops and takeaways. But, there is the fascinating piece of information that it is Cambodian refugees since the 1970s who own and staff so many of these donut stores.

And, from icing exuberance we suddenly move to the history of Cambodia in the first half of the 1970s – the Vietnam war, its extension into Cambodia, Nixon and the extensive bombings, stopped by Congress, the rise of the Khmer Rouge, the massacre of populations, the enormous migration out of Cambodia, the status of the country by 1976 and the devastation of Phnom Penh. All presented powerfully and with a great deal of contemporary news footage.

So, this is not just a sweet and tasty documentary.

We are introduced to a refugee, Uncle Ted Ngoy, and his wife, children and extended family. Ted Ngoy served in the Cambodian military in Bangkok and is accepted as a refugee in the United States. In interviews for the film, Uncle Ted, 77 at the time of filming, backgrounds what happened in Cambodia, his extraordinary success with the donut market, and his ability to sponsor many Cambodians taking refuge in the United States. The Cambodians, as with the Vietnamese after the fall of Saigon, are nothing if not industrious (which might not give true acknowledgment of their seven-day a week, no holiday, commitment to their work and to the saving of money for the benefits of their family).

One of the commentators is a food and recipes’ journalist, who comments on this phenomenon of Cambodians and donuts, especially in California. There are also interviews with the executives of Dunkin’ Donuts, Winchells, and other franchises, which turns the documentary into something of a story of the successful American dream. Other members from the Cambodian community are also interviewed, including Uncle Ted’s wife, Christy, a vivacious personality, who reminisces about fleeing Cambodia, the flight, the camp, and her horror at being fed mashed potato and pasta.

One of the key features of the documentary as it looks back at the 1970s is the contribution of President Gerald Ford and his welcoming of the refugees, despite the apprehensions of California Governor Jerry Brown about jobs and workers. (The implication, sometimes explicit, is that Americans in those times, despite fears and some xenophobia, were more welcoming than present America is to refugees.) Uncle Ted and his family were sponsored by a Lutheran parish reminding audiences of welfare groups, churches, and welcoming migrants, remembering that the United States was built on migrants.

One of the shocks of the film – and, therefore, not to be in included as a spoiler here – is that everything did not go smoothly for some of the migrants, which makes the story of The Donut King, a rather more complex tale than simply a fairytale interpretation of the American dream.

Donut fans will be glad to know there have been extraordinary adaptations since the 1970s, with Americans eating billions of donuts per year, an increasing range of designer donuts – and the visuals do not let up until the final credits.