Have you ever noticed when you slice a carrot that it looks like a human eye? Or that the deep red juice from a beetroot resembles human blood? Or when you crack open a walnut it looks just like a brain?

In our early folklore, with remarkable frequency in cultures all over the world, the idea grew that the signature of a plant - be it the shape, colour, form or even taste - could be used to divine its medicinal properties.

North American Indians used black cohosh and wild indigo as snake medicines because the seeds in the seedpod produce a rattling sound. They also thought that the stalks of common purslane, which resemble worms, could be used to treat worms in humans. In ancient India, plants with a yellow flower were recommended for the treatment of jaundice.

Dioscorides, who practiced and wrote about medicine in ancient Rome, was one of the first to describe a plant signature in the year 65: "The Herb Scorpius resembles the tail of the Scorpion, and is good against his biting."

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The idea took hold and was penned during the Renaissance as the Doctrine of Signatures, based in the idea that the features of plants resemble, in some way, the condition or body part that the plant can treat. So, bloodroot's scarlet roots could treat diseases of the circulatory system, while the bud of a peony, which looks like a human skull, was used as a remedy for epilepsy and brain injuries.

We now know it's obsolete as a medical theory, if not downright dangerous - mushrooms, for example, may look like an ear and so might have been assumed to treat earache, but choose the wrong mushroom and it may well be your last meal.

The current thinking around the Doctrine of Signatures is that it was a good way to remember cures, and in that way was useful for early peoples who did not have a written language. Yes, eating carrots will help your eyesight, as they are a good source of the carotenoids that support eye health. And beetroot juice, a powerhouse of antioxidants and phytochemicals, is considered a blood cleanser.

The botanist William Coles wrote that walnuts were good for curing head ailments because, in his opinion, "they have the perfect Signatures of the Head". A recent study published in The American Journal of Nutrition, Health and Aging found that walnut-eaters scored significantly better on a series of cognitive tests, variously measuring everything from reaction time to story recall. It is thought that this may be related to the walnut's high content of antioxidants and omega-3 fatty acids. It's a no-brainer really!

Leafy Salad with Walnuts and Blue Cheese

Ready in 15 mins
Serves 4-6

½ cup walnuts
6 handfuls (about 150g) mixed salad greens, washed and dried
60-80g blue cheese, crumbled
Dijon Mustard Vinaigrette
2/ 3 cup extra virgin olive oil
3 tsp lemon juice
1 Tbsp wine vinegar
1 tsp dijon mustard
1 tsp sugar
½ tsp salt
ground pepper, to taste

Preheat the oven to 180C fanbake. Place the walnuts in an oven dish lined with baking paper and roast them for 10 minutes until toasted but not blackened.

While the walnuts are roasting, make the dressing by combining all ingredients in a small jar and shaking to emulsify. Taste and adjust ingredients to your own taste. If it's too acidic add more oil, too sour add more sugar - you're aiming for a pleasant balance of flavours.

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Put the salad greens in a large serving bowl and sprinkle with the toasted walnuts and the blue cheese. Just before serving, drizzle about ¼ cup of Dijon Mustard Vinaigrette over the salad and toss to combine. Store the remaining dressing in the fridge as a head-start on your next salad. It will keep for weeks.

Annabel says: Roasting walnuts brings out their sweetness and delivers a wonderfully crisp texture. Blue cheese, leafy greens and juicy pears are perfect partners in this winter salad. I always make extra dressing so I can keep the extra in the fridge.

Walnut Pastila

Walnut pastila. Photo / Annabel Langbein Media
Walnut pastila. Photo / Annabel Langbein Media

Ready in 30 mins + chilling
Makes 2 logs

2 cups pitted prunes, coarsely chopped
1 cup sugar
¼ cup honey
finely grated zest of 1 orange
½ cup fresh orange juice
2 cups walnut pieces, pistachios or toasted, skinned hazelnuts
¾ cup desiccated or thread coconut

Place prunes, sugar, honey and orange zest and juice in a pot and bring to a boil. Cook, stirring, over a medium heat until the prunes are soft and the mixture comes together into a paste (about 10 minutes). To check whether it's ready, place a small spoonful in a bowl of iced water or in the fridge for a couple of minutes - it is ready when it's firm enough to be moulded, like toffee to soft-ball stage. Remove from the heat and stir in the walnuts.

Divide the coconut between two pieces of baking paper. When the mixture is cool enough to handle, divide it in half and form two evenly shaped logs, each about 30cm long. Roll in the coconut to coat, then roll up in the baking paper and refrigerate until set. Slice thinly to serve. Pastila keeps for a couple of months in a sealed container in the fridge or can be frozen.

Annabel says: This rich Middle-Eastern sweetmeat makes a great after-dinner treat, and is a lovely gift to take to a dinner party. It's great with any combo of nuts - try a mixture of pistachios and hazelnuts for a change.

Walnut Oat Biscuits

Walnut oat biscuits. Photo / Annabel Langbein Media
Walnut oat biscuits. Photo / Annabel Langbein Media

Ready in 40 mins
Makes about 40

½ cup walnut pieces
2 cups rolled oats
¾ cup wholemeal flour
¼ tsp baking soda
1 tsp salt
3 tbsp sugar
100g butter, at room temperature
1 egg
2 tsp boiling water

Preheat oven to 160°C fanbake. Line 2 baking trays with baking paper.

Place walnut pieces in a food processor and whizz to a crumb. Add all remaining ingredients and process until mixture forms a soft, sticky dough. If too dry and not holding together easily, add another teaspoon or two of boiling water.

Use lightly floured hands to roll walnut-sized balls of dough. Place on lined baking trays and press flat. Bake until golden and crisp (20 minutes). Cool on trays then store in an airtight container. They will keep fresh for weeks.

Annabel says: Thanks to their high fat content, walnuts are prone to rancidity so shelled nuts should be stored in the fridge or freezer. However, if left in the shell, they will keep fresh for months.

Essential Annabel Langbein (Annabel Langbein Media, $65) is a beautiful compendium of Annabel's best-ever savoury recipes and cooking tips and it's on sale now at Paper Plus, Whitcoulls, The Warehouse and all good bookstores. Find out more at annabel-langbein.com or follow Annabel on Facebook or Instagram.