Buttermilk can bring something really interesting, both in texture and in taste, to all kinds of dishes.
Like parents, cooks shouldn't have favourites, but some recipes inevitably shine more than others. One that stands out for me is a buttermilk-crusted fried okra dish with a tomato and bread sauce that I wrote about here a couple of years ago. Thanks to the buttermilk in it, the batter was magically light - silky, almost.
Though more commonly found in breads or cakes, buttermilk - the tart, slightly sour-tasting liquid made by fermenting milk or from making butter - can bring something really interesting, both in texture and in taste, to all kinds of dishes. It turns mashed potato, say, into the kind of velvety bed that pretty much anything would be happy to lie on, especially if you underpin the buttermilk's natural sharpness with some grated parmesan and lots of seasoning.
Buttermilk's palate-cleansing tartness is one reason it's used a lot in southern India, where meals often end with a small bowl of the stuff served with plain rice and pickles. And in northern India it features in chhas, the popular breakfast and lunchtime drink made by mixing roasted and ground cumin seeds with cold buttermilk, a pinch of salt, pepper and cayenne. I use it most frequently in dressings for salads and roasted vegetables, when I want to keep things light.
Buttermilk is naturally low in fat (the cultured variety is made from fermented skimmed milk), so it's a favourite tool among the health-conscious for tenderising chicken. Make a simple marinade of half a litre of buttermilk, five crushed garlic cloves, a tablespoon of Dijon mustard and half a tablespoon of soy sauce, pour over skinned chicken pieces, and leave the enzymes and acids to do their job overnight - the chicken, once roasted, will be almost achingly soft.
Buttermilk's qualities can also be harnessed for puddings: Angela Hartnett's guilt-free version of panna cotta combines single cream, buttermilk, apple juice and gelatine, lending the classic dessert a saintly silkiness. My recipes today do not make the most of these health credentials, but they do highlight some of the reasons buttermilk is one of my favourite ingredients.
Buttermilk and bay leaf tart
Serve with crème fraîche and a simple plum or gooseberry relish: just simmer the fruit with some sugar and vanilla until it's reduced to a consistency slightly runnier than jam. Serves eight.
285ml buttermilk (ie, one standard supermarket tub)
100ml double cream
15 bay leaves
50g melted unsalted butter
180g caster sugar
2 tbsp plain flour
½ tsp grated lemon zest
For the pastry
150g plain flour
¼ tsp salt
80g cold unsalted butter, cubed
35ml ice-cold water
First make the pastry. Mix the flour and salt in a large bowl, then add the butter and, with your hands, rub in until it resembles breadcrumbs. Stir in the water and bring the mixture together to form a dough. Stop mixing as soon as it comes together, wrap in clingfilm and store in the fridge for at least two hours.
Meanwhile, put the buttermilk, cream and bay leaves in a medium saucepan. Place on a very low heat and simmer for about 10 minutes, stirring all the time, making sure the buttermilk does not boil and split. If you have a thermometer, use it to check that the milk is not going above 70C. Leave to cool for at least an hour (or overnight, if you have time), then remove the bay leaves and stir in the melted butter.
Heat the oven to 170C/335F/gas mark 3. Roll out the pastry into a 32cm-diameter circle. Very lightly grease a fluted tart tin that's 24cm in diameter with a 4cm edge, and line with the pastry. Chill for 30 minutes, then line with parchment paper, fill with baking beans and bake for 25 minutes. Remove the beans and paper, bake for another 10 minutes until golden, then set aside to cool.
Raise the oven temperature to 180C/350F/gas mark 4. Whisk together the eggs and sugar until light and airy. Fold in the infused buttermilk, followed by the flour and lemon zest, and mix gently until smooth. Pour into the pastry shell and cook for 30 to 35 minutes, until just set. Remove from the oven and leave to cool down. Take out of the tin and serve at room temperature.
Johnnycakes with smoked trout and horseradish
While I was in Boston earlier in the year, I had my first taste of New England johnnycakes, a kind of cornmeal pancake with a subtle flavour but a wonderful creaminess that is an ideal companion to fish and seafood. The mustard and horseradish here are wonderfully fiery and go well with the mild cakes, but reduce the quantities a little if you prefer. Makes eight pancakes, to serve four as a starter.
10g chives, finely diced
10g fresh horseradish, grated
1 celery stalk, very finely diced
½ tbsp mustard powder
1 tsp grain mustard
80g sour cream
½ tsp caster sugar
½ tbsp white-wine vinegar
150g hot-smoked trout, crumbled into big chunks
About a ¼ cucumber, unpeeled, seeds removed and chopped into 0.5cm dice
1½ tbsp sunflower oil
Baby cress, for garnish
1 tbsp olive oil
1 lemon, cut into wedges, to serve
For the johnnycakes
190g quick polenta
20g plain flour
1 tsp celery seeds
1 tbsp caster sugar
1 tsp baking powder
25g melted butter
1 egg, separated
In a medium bowl, whisk the chives, horseradish, celery, mustard powder, grain mustard, sour cream, sugar, vinegar and an eighth of a teaspoon of salt. Gently stir in the trout and cucumber, and set aside.
For the pancakes, mix together all the dry ingredients in a large bowl and add a quarter-teaspoon of salt. Whisk in the buttermilk, butter and egg yolk. In a separate bowl, whisk the egg white until soft peaks form. Fold the egg white through the pancake mixture.
Put a large frying pan on a medium flame. When it's hot, add half the butter and sunflower oil. Making three to four pancakes at a time, 10cm in diameter and 1cm thick, cook for two to three minutes, flip and cook for another minute or two. Put on a plate lined with kitchen paper, keep warm and repeat with the rest of the butter, oil and pancake mix.
To serve, put two pancakes on each plate and top both with a generous dollop of trout mix. Sprinkle over some baby cress, drizzle on a little olive oil and serve with a lemon wedge.
• Yotam Ottolenghi is chef/patron of Ottolenghi and Nopi in London
Yotam Ottolenghi's buttermilk and bay leaf tart: 'Buttermilk is one of my favourite ingredients.' Photograph: Colin Campbell for the Guardian