For a cook and baker of such an upbeat and optimistic outlook on life ("I'm a Libran and like everyone to be happy," she says), Sue Lawrence's first novel has a rather dark edge to it.

Almost as dark, in fact, as one of her famous spiced brownies. Her characters - one lot set in modern times and the other in 19th century rural Tayside - gradually become caught up in family secrets as sticky as her caramelised onion marmalade. Even the author admits to being "quite surprised" to find how naturally the dark side came to her.

It's all too easy to make endless similes with making fiction and making food, but I don't mean to sound trite when I ask Lawrence, a BBC MasterChef winner in 1991 and author of many books on cooking and baking, if there is a parallel with creating and testing recipes and plotting and writing a novel. Fields of Blue Flax, a rich story whose ingredients contain female jealousy, betrayal, deception and revenge, is especially complicated, since it involves the dual narrative. For the reader it's utterly compelling; for the writer, it took two-and-a-half years, including a six-month cooling off period (no pun intended). Her next novel, Window on the Tay, is set in 1879 Dundee and centres around the Tay Bridge disaster with a chef as one of the protagonists. It too has a dual narrative and will be published next spring.

"Writing fiction is far more personal than writing recipes," she begins. "It's a different kind of creating from cooking. Fiction is like baring your soul, even though my characters are nothing to do with me or my family.

"When you make a recipe on the other hand you're taking the basic ingredients, writing them down, then you cook it and it's tangible, then you eat it and it's gone, finished. With fiction, it stays with you. Lots of people tell me my characters are still with them. I think fiction does have the potential to hang around, whereas a recipe doesn't so much."

The lingering taste of a memorable dish does, of course, live on in the memory, and Lawrence, an advocate of traditional Scottish cooking, sprinkles her novel with liberal references to Scotland's ancient diet. These include ramson (wild garlic) soup, a slow-braised leg of mutton a la francaise, mutton broth cooked in a pot on a swee over the fire, soups flavoured with cow heels, leek and tattie soup, oatcakes and wild mushrooms. Modern dishes cooked by the two protagonist cousins who begin to research their forgotten relative, include chicken roasted with 40 cloves of garlic the French way, buttered scones, homemade jam of local soft fruits, and brownies. The brownies feature often in the novel, and act as a leitmotif signalling both pleasure and danger - though I am not going to give away the entire plot.

It's a highly engaging read, and the constant references to food throughout the unravelling of various lives, in the present and in the past, underline how eating is linked to a range of human emotions through history.

A dab hand at reviving traditional Scottish recipes and putting a modern twist on them in books such as A Cook's Tour of Scotland and Scottish Baking (in which she adapts a 1701 recipe for plum cake which contained preserved quince, mace and other spices, two dozen eggs, sweet cream and Sac, an early Vermouth), making things as straightforward as possible for readers comes as second nature to Lawrence. Her training in such valuable discipline began early, as a trainee journalist at DC Thomson in her home city of Dundee. She recalls that when writing for My Weekly magazine, she was reprimanded by no other than Mr Thomson himself for using a word that contained more than two syllables. "I think it was 'lackadaisical' or something, but whatever it was it was deemed unsuitable for the My Weekly readership," she says. "It was a good lesson to learn."

Sitting in her large, sunny and extremely tidy Edinburgh kitchen overlooking her well-tended garden, we're munching delicious newly-baked brownies lightly spiced with cardamom and cinnamon. Both the location and the cookies echo parts of the plot in her novel, a fat that seems to crystallise Lawrence's dual powers of logic and creativity as well as discipline. She attended a creative writing course with tutors Sue Peebles and Alan Warner, which she says was invaluable.

It's in this room, while cooking, that she has had many ideas for her plot. A graduate in Modern Languages from Dundee University, she acknowledges she has both, but reckons her creative mind is stronger. The learning of another language or two is good for both parts of the brain; she lived in Lourdes for a year as an undergraduate English assistant in a French lycee, and did a 10,000 word dissertation on Lourdes: Religion or Commerce? She also spent three months as an au pair in Provence. On top of that, she lived near Bremen for three years when her RAF husband Pat was posted there. She "gave birth in German" and can still remember certain verbs related to breathing fast and keeping her newborn son warm. Keeping up her languages and playing piano (another narrative thread in her novel) are great disciplines for keeping the logical mind active, she believes.

This all helped with the development of her novel (the third one she's written in five years, but the first to be published). "The narrative evolved, I didn't have the vision to know what was going to happen," she says. "When you start researching old relatives' lives you start at a wedding, then find the parents and then the grandparents' deaths, and keep going back as far as you can. For a narrative it's quite unusual to go back like that, and as a structure it's quite complicated to do. You're trying to remember what readers know, and if the dates all match as they are not all chronologically plotted. You ask yourself, 'does somebody know that has happened yet?' To write both stories together is quite a challenge for me, but hopefully not for the reader."

It's true that Fields of Blue Flax brilliantly evokes rural Tayside, its large 18th century country houses and the traditional rural way of life; blue flax was an attractive feature of the area because it was needed for the linen and jute production up until the 19th century; it doesn't grow any more. Now the fields are covered in bright yellow rapeseed - a sight not as pretty as Lawrence imagines the blue flax would have been. She's not so keen on the bright yellow fields of rapeseed flowers, though she does sometimes use Scottish rapeseed oil for cooking.

She does use wild garlic when in season, though there is nothing much to differentiate it from the lethal leaves of Lily of the Valley, which comes into season around the same time. This duality is another theme in the novel, and illustrates how the two faces of Mother Nature are interchangeable.

I stop and stare at my half-eaten brownie, suddenly aware of a bitter-sweet irony. We both laugh uproariously.

Fields of Blue Flax is published on May 11, 2015, by Freight Books, priced at £8.99.